It goes down like this.
After everything is said and done, after all the world-ending threats are gone and life returns to normal, Castiel is given a choice. Come back or stay here. Continue with the life he's lead for time out of mind or clip his wings and tie himself to the ground, become a creature of dust and blood and bone. The discussion between Castiel and whoever's actually in charge up there would be far too destructive for Dean, whose ears and eyes still can't see and hear angels, even with everything else he's seen. So he waits in a humid motel room in Santa Fe with Sam and tells himself that Castiel will come and say goodbye before he goes back to Heaven for the last time. He doesn't let himself think that Castiel will choose Earth, choose him, because Dean knows it'll hurt like a bitch for Cas to leave his family and he doesn't want anything to hurt Castiel ever again.
So when Castiel appears in the center of the hotel room, fixes his wide shocky eyes on Dean and says, "Oh," Dean feels his heart plummet.
Then Castiel keels over in a dead faint and if he weren't unconscious, Dean would punch him because of course Castiel chose the hard path. He's practically a Winchester now and what Winchester doesn't do things the difficult way?
When Cas wakes up twelve hours later, he smiles at Dean and asks if he could stay with them for awhile. Dean rolls his eyes and climbs into the bed with him. This is his answer because it's too much, too soon to say, 'stay forever.'
Dean figures there'll be a lot of repercussions of Castiel becoming a human. Lots of emotional trauma and fits of depression. And there is, to a certain extent. Sometimes Dean catches Castiel staring. Just staring into an empty space. He never cries in front of Dean, but every so often, after a very long shower, Dean notices that Castiel's eyes seem too red to be the fault of steam and heat. Dean never says anything about it, but on those nights, he holds Castiel extra tight while they lay in bed.
So, yeah, he expects those things. Dean knows a lot about giving up your life for someone else, so he expects the emotional roller coasters and he's ready for it. He's ready to do whatever Castiel needs because Castiel would do the same for him and because Castiel deserves everything Dean can give him.
What he doesn't expect are the physical changes.
Okay, correction. Dean expects some of the physical changes. When he climbs into that bed with Castiel the first time, Dean's stomach flutters in anticipation of their first kiss, of Castiel's newfound ability to respond to Dean's touches in a way he never could before. Castiel's a terrible kisser, but he gives all his kisses to Dean, so Dean is a patient teacher. Soon enough, Castiel becomes an expert at kissing or at least an expert at kissing Dean and really, that's the only kissing he needs to know, as far as Dean's concerned.
But it's not just the kissing and hugging and other pleasant activities that Dean expects. He also expects the sleeping and the eating and the need to bathe. He expects the danger, the new fragility of Castiel's human flesh. He and Sam spend a great deal of time training Castiel, teaching him how fight with his hands and his body, how to fight without his angelic powers. Castiel is a quick learner, though easily frustrated by his diminished capacities. Whenever he gets discouraged, Sam reminds Castiel that Dean saved the world with nothing more than his mind and muscle and while it makes Dean feel weird to hear it, the sentiment always manages to calm Castiel and firm his resolve to perfect the latest fighting move.
The point being, that it's not quite fair to say that Dean didn't expect some of the bad side effects. He just didn't expect quite so many.
The first unexpected side effect of humanity they encounter isn't so serious. In fact, it's not really bad at all, just surprising and disconcerting.
On their second night together, Dean is shocked awake by a high pitched whining sound. Before he can react, he is pushed to the edge of the bed and with a yelp, crashes to the floor, landing hard on his ass.
"Ow, what the...?" For a second, Dean lays where he lands and lets the pain wash over him. Then he shoots up, ignoring the throbbing ache in his lower back and glares at Castiel, fully prepared to be pissed. Instead, what he sees sends a shiver of panic down his spine.
Castiel is standing beside the bed, ramrod straight, staring ahead into the darkness of their room.
"Castiel?" Dean tries again. As Dean watches, Castiel steps forward, seemingly ignoring Dean and walks into the bathroom. Standing himself, Dean follows, eyes widening. Once inside the bathroom, Castiel shuts the door, flicks on the light and begins undressing. Dean is afraid to touch him, afraid to wake him because he can't remember if you're supposed to wake up sleepwalkers or not.
Dean blinks. Castiel, former angel of the Lord, is a sleepwalker.
A sleepwalker that's soon stripped down to nothing and Dean wonders if it's wrong of him to enjoy this part of the ordeal so much. He considers leaving, but he's afraid that Castiel will hurt himself. So, Dean finds himself standing outside a small shower stall at 3:30 in the morning, watching his sleeping lover thoroughly bathe himself. Much later, long enough for Castiel to develop pruny fingers, he shuts off the shower and travels slowly back into the main room. He stops at their dresser and fishes around inside until he finds a pair of Dean's pajama pants and an old t-shirt of Sam's that somehow ended up in their things. He dresses, shirt hanging down past his groin, and just like everything is back to normal, Castiel puts himself to bed, snuggling into Dean's pillows and breathing a deep sigh of contentment.
The next day, Castiel has no memory of the shower at all.
It's strange, but they can deal with it, Dean figures. Some research tells Dean that it's safe to steer Castiel back to bed and for the most part, it seems to do the trick.
The next problem they discover is a lot less pleasant for Castiel.
Dean can't help feeling guilty for Castiel's fall. Even though Castiel tells him he doesn't regret it and that Dean makes him happy, Dean still knows it's his fault that Castiel is stuck away from his family. So, he decides it's his job to introduce Castiel to all the fun parts of being human. Of course, love and physical affection is covered first. This is quickly followed by food consumption. Of all the constant nagging Castiel receives from his new body, he dislikes hunger the most. His first meal is soup and crackers because he's still feeling a little queasy from whatever it is that the angels did to make him human. Dean wishes it could be something more exciting, but apparently, Castiel really likes chicken noodle soup, so he figures that's fine.
This doesn't mean he doesn't take Castiel to a good restaurant once he's feeling better. He orders Castiel the highest quality steak on the menu, along with a salad, a baked potato and of course, a piece of rich flaky peach pie. Castiel's not quite up to finishing it all, but he loves everything he tries and Dean's a little embarrassed by how pleased this makes him. So pleased in fact, that he doesn't notice the looks they're getting from the other customers until Castiel points it out and that's when Dean realizes they are on their first real date.
Dean tells him they are just jealous. It might have bothered him years ago, but really, once you've nearly seen the world end, the opinions of strangers hardly matter.
Their great food experiment goes downhill during lunch the next day. Castiel insists on going to the sort of diner that Sam and Dean frequent while on hunts. He's curious about the type of food that brings the brothers back time and again and so they find a little eatery in downtown Santa Fe that promises the world's juiciest burgers. When Castiel asks, Dean explains that they might not actually be the world's juiciest burgers. Castiel is bothered by the fib, but they convince him it's a natural part of advertising and so thirty minutes later, Castiel is sitting in front of a cheeseburger that indeed rather juicy, a pile of French fries and a large chocolate milkshake.
It's the milkshake that's the real success. It's Castiel's first taste of chocolate and judging by his expression of surprised ecstasy, he approves heartily. Sam teases him about a sweet tooth, Dean praises him for his good sense and they all leave the diner feeling rather good about life.
Until the rash breaks out on Castiel's neck and arms.
Dean notices it first when he glances at Cas in the Impala's front mirror, even before Castiel is aware of the niggling itchy sensation developing on his skin.
Castiel jumps and Sam spins around, eyes going round with horror as he sees the patchy scarlet hives spreading along Castiel's arms with alarming speed. Castiel stares down at his hands and blinks slowly. When he looks back up at the Winchesters, Dean can tell he's having trouble forming coherent thought. "My head hurts," he comments absently.
"Sam, hospital," Dean spits out, fear closing his throat against the words and Sam's whips out his phone, frantically searching for the closest medical center.
They pull into the emergency lane fifteen minutes later and by then, Castiel is dizzy and inarticulate, mumbling nonsense and scratching at the ugly red marks that have arisen on his chest. Sam jumps out, opening doors ahead of Dean, who pulls Castiel out of the car and nearly carries him into the ER. A doctor appears out of nowhere, asking if Castiel has any known allergies and Dean and Sam can only gesture soundlessly, helplessly. A nurse tries to stop Dean from following the doctor into the treatment area, but Dean refuses to be pushed back. He forces his way through, leaving Sam to deal with the nursing staff. Once the gurney settles again, Castiel shrinks back from the doctor's hands, his confusion and fear making him erratic and dangerous and when he calls for Dean, nothing is enough to stop Dean from coming to his side.
"It's ok, Cas, I'm here. You gotta calm down, man. The doctor's gotta look at you," Dean babbles. He's not sure if Cas is really hearing him or just responding to his voice, but he quickly begins to settle and calms even further when the doctor gives him a shot of something.
"Mr...?" The doctor looks expectantly at Castiel. It's the first time anyone's asked Castiel for his name and it occurs to Dean that they'll have to get to work producing faked documents to prove Castiel's existence in his new life.
"Castiel," he says.
"Mr. Castiel, I need to know what you've eaten today," the doctor says. Dean tunes out their conversation in favor of stroking Castiel's neck and watching in relief as the hives begin to recede. He tunes back in when the doctor tells Castiel she needs to draw some blood and Castiel flinches. It's an odd reaction for someone who once sliced his arm open and poured out what seemed like gallons of blood to protect Dean from Zachariah. But Dean doesn't question it, just takes hold of Castiel's hands and murmurs more nonsense in his ear while the doctor finds a vein in Castiel's arm and sticks a needle deep under his skin, drawing out several vials of blood.
She leaves them alone, promising to return as soon as possible with a diagnosis. Castiel heaves a sigh and turns to look at Dean.
"I don't like this," he says.
"Yeah, me either," Dean agrees.
By the time she returns, Castiel is asleep, snoring lightly. She tells Dean quietly that, "Your partner is allergic to cocoa. It's really quite rare. I've never actually seen a case myself. It's a powerful allergy, judging by the rapid reaction. He'll have to swear off chocolate." She pauses, then gives Dean a curious look. "He must not eat chocolate very often to not know about this reaction. He must be, what? Thirty-five?"
Dean shifts in his chair. "Sure," he says. Thirty-five...thousand or million or billion, he doesn't really know. He's never thought to ask how old Castiel truly is. "About."
"Well, it's not exactly uncommon to develop food allergies later in life," she continues. "But like I said, this one is pretty severe. I can prescribe some meds, but I recommend he just stops eating chocolate altogether."
The guilt swells up again. Just when Castiel finds something he really loves, his delicate human body takes it away from him. Dean swallows hard against the lump forming in his throat and nods, brushing fingers through Castiel's sweat dampened locks.
Castiel accepts the news about his food allergy calmly. "I don't like the hospital," he confides to Dean later that night, under the covers. "I would rather just not eat chocolate than make another visit."
"Okay," Dean says and kisses him, relieved at Castiel's decision. It's not that he's surprised that Castiel's sudden illness scared him. It's how much it scared Dean. It's still inside him, rolling in his stomach, making him hold Castiel closer, longer. It's the kind of fear he's always reserved for Sam only and Dean doesn't want to feel it ever again. So, as his tongue traces Castiel's mouth, Dean silently vows to pay more attention and keep Castiel out of pain as much as possible.
They end up at the doctor again less than a week later.
The only thing that keeps Dean from punching a wall is that it's not for something that has Castiel in actual physical pain.
Dean begins to suspect something's wrong with Castiel's hearing when he finds himself occasionally repeating a sentence here and there for him. Nothing out of the ordinary really, but once it happens for the sixth time, Dean begins to wonder. His suspicions grow when he comes out of the shower one day and Castiel has the television on so loud that it's a wonder the neighbors haven't come to complain.
"Is it loud enough?" Dean asks, going over to turn down the volume. The bewildered expression on Castiel's face does nothing to calm Dean's nerves.
"I'm sorry," he says. "I didn't realize it was so loud."
Dean just shrugs, but he begins to pay attention, making note of every time Castiel seems to miss something Dean or Sam says. He starts testing Castiel by making quiet remarks at his side and seeing if Castiel hears him. Castiel responds only about half the time. It's when Dean begins to wonder if Castiel is so loud in bed because he doesn't realize how loud he's actually being that he finally brings it up to Castiel.
"I thought it was part of becoming human," Castiel confesses. "But you think it might be a problem?"
Resisting the urge to strangle him, Dean only nods. "Cas, you have to tell me if you can't hear, ok? You gotta tell me if anything hurts or is uncomfortable or hard to deal with, ok?"
"Alright," Castiel agrees. "In that case, I would rather you didn't sleep on my arm at night. It's feel odd in the morning."
Dean rolls his eyes and flips open a phone book, searching for an ear doctor.
The next day, at their appointment, where Castiel presents himself as Mr. Castiel Smith, complete with authentic looking papers, the doctor tells them that Castiel suffers from moderate hearing loss. He says that the damage he sees in Castiel's ears suggests that Castiel must have been subject recently to a very loud noise. Dean and Castiel exchange a glance. Castiel doesn't remember much in between telling the archangels his decision to become human and showing up in Dean's motel room, but it now seems possible that Castiel was human within hearing range of the archangels long enough to sustain damage.
Dean's hands curl into angry fists, but he says nothing in front of the doctor, takes the comfort of Castiel's fingers closing over one fist and squeezing. Castiel and the doctor discuss hearing aids and a week later, Castiel is fitted with a pair of small hearing aids, the kind that are hard to see at first glance. The look on Castiel's face when the aids first begin to work is priceless. His eyes pop wide open and his lips part in surprise.
"Oh," he says, sounding much like he did after he first became human.
"Is it ok?" Sam asks nervously while Dean hovers silently in the background.
Castiel turns a huge smile on Sam and nods. "Your voice, it's not muffled anymore." With growing excitement, he turns to Dean. "Say something. I want to hear your voice."
"Oh, um. Hey," Dean says, feeling foolish. "How's it going?"
A wispy sigh of pleasure falls from Castiel's lips on a long exhale and he twines his fingers through Dean's. "Much better now."
Dean forgets his anger and guilt for awhile that night when he discovers that Castiel's hearing problem had nothing to do with his loudness in bed. In fact, his volume level seems to increase and he confesses to Dean later that it's because he can now hear all those little moans and sighs that Dean had been making all along.
Which is pretty awesome, but it doesn't stop Dean from feeling awful that Castiel had to go through any of it in the first place. When Sam suggests that the three of them go out for a day of fun at a local state park, Dean quickly agrees. Castiel hasn't had much chance to enjoy the great outdoors with his new sensory capacities and they could all use a day to just hang out together. Sam packs them a picnic lunch while Dean scrounges up a couple of blankets and they set off. Castiel is interested in hiking and while Dean isn't much for it himself, he isn't about to shoot down any of Castiel's ideas, so they set off. After carefully applying bug spray, of course. Dean's not about to chance setting off another allergic reaction.
It's a beautiful day with sky of blue and clouds of pure white streaming across the horizon. It's hot, but the good kind, with low humidity. Castiel clearly revels in being outside, being closer to God he tells them when they stop for lunch and Dean pats Sam on the back for his good idea.
It's when they are walking back down the mountain in the late afternoon that Dean realizes Castiel's face looks a little redder than usual. For a moment, he panics, thinking he's seeing hives breaking out again, but then he realizes that Castiel's skin isn't bumping. It's just turning a deep scarlet red.
"Oh shit," Dean mutters. Sam and Cas turn to him, curious and Dean briefly considers pounding his forehead against the nearest tree.
Later that night, Dean helps Castiel take off his clothes as slowly as possible and lays him out on the bed. The burn is worst on his chest and face, so he lays on his back, face scrunched up in pain.
"This is incredibly uncomfortable," he says and Dean winces in sympathy as he smears great globs of aloe across Castiel's dry and now crimson red chest. It's been awhile since Dean had to worry about sunburn. When they were kids, Dean remembers his father grabbing him before he went outside and slathering a bunch of kiddie sunblock on his skin. And once he grew up, Dean really spent more time outside at night, chasing down the sort of evil creatures that prefer darkness.
"I'm sorry," Dean chokes out and he knows he means for more than the sunburn. It's for the sleepwalking and the bad hearing and the allergic reactions and all the undignified human crap Castiel has to endure now because of Dean. Because he loves Dean. "I should have known."
Castiel grabs Dean's hands, ignoring the slick aloe on his fingers and draws them to his chest, laying them on his heart.
"You couldn't have known. You can't stop me from being hurt, Dean," Castiel says.
The fear swells in Dean's chest, like after the hospital trip, growing and pushing, painful and intense. "I should be able to-"
"No." Cas sits up and cups Dean's chin in his palm. "I chose this life. All of it, Dean, the bad and the good. I'd rather have trouble hearing and trouble sleeping and everything unpleasant humans must deal with than be in a perfect body without you."
It's too big again, too much, no one can love him that much. Dean shakes his head against the words in his throat because he doesn't know how to say them or what they even are, except he needs Castiel to understand that he's not worth this much trouble. "I'm sorry," he says again and tries to look away, but Castiel stiffens his grip.
"I'm not," he says, blue eyes locked onto green, deadly serious and despite himself, Dean feels the bands around his chest ease just a tad. "I'll never regret you."
"Bet you're regretting the hike though," Dean jokes weakly, unable to endure the heaviness between them. Castiel smiles too and Dean loves him a little bit more for letting Dean get away with lightening the mood.
"Well, perhaps next time we'll bring some sunscreen," he allows and drags Dean's slippery hands to his chest. "I had no idea human skin could feel this raw," he complains. Dean pushes him back down and gets back to work, drawing designs across his chest and arms in green.
"I love you," Dean say suddenly, startling himself. It's the first time he's ever said it and he'd meant to plan it a bit better. But then Castiel's expression turns awed and beautiful, so Dean can't regret it.
"I love you too, Dean," he answers.
"In sickness and in health," Dean say absently, then bites his tongue. Luckily, Castiel doesn't get the reference. He just pulls Dean down into a kiss.