It gets worse after Bobby dies.
Sam tries everything to keep it together. He has to, for Dean - Dean, who's falling deeper and deeper into the bottle and running himself ragged trying to avenge Bobby. It's not that Sam doesn't want to kill Dick Roman too - he does, he just knows that going up against him would be a suicide mission. He's worried that's why Dean is so intent on it.
Sam's hallucinations have been getting worse. He hasn't told Dean, because - what's the point? For the most part, he's got a handle on them. He ignores Lucifer - doesn't talk back to him at all anymore. When the world melts away and his feet step through the earth and into hellfire, he keeps right on walking, flinching only slightly at the feeling of his flesh burning.
Lucifer, (Sam's hallucination of Lucifer),doesn't take kindly to being ignored. At all. He starts grabbing Sam - keeping him from moving, staring into Sam's eyes like if he just looks deep enough, Sam will finally accept that he's real.
There are times when Sam stops walking mid-stride, because Lucifer is pushing against his shoulders. The imaginary Devil is as immovable as a fortress, and Sam can't do anything but wait until the grip fades and he can walk again.
Lucifer appears every hour, of every day...but Sam keeps ignoring him. Until one day, while Dean is deep asleep, Lucifer doesn't appear in front of Sam, he appears inside of him.
Sam watches in horror as his hands, arms and legs move against his will. Lucifer stretches languorously, and walks over to the mirror. He runs his hand down Sam's chest, and sides, and grins saying, "Man - it is good to be back."
Sam screams from inside his own head, and tells himself over and over that he's just having a worse hallucination than usual. "You're not real. You're not real." he says - over and over, like a mantra.
Lucifer laughs, loudly, "Oh come on, Sam. You know I am. You do remember, don't you? You said 'yes' to me - no take-backs. We're bound. We are two halves of the same soul. You may have locked me back up, and my grace might still be down in the Cage, but that doesn't mean I'm cut off from you. Nothing in the universe can keep us apart forever, Sam. Nothing."
Sam watches in horror as Lucifer walks out the door, gets into their car, and drives away.
He fights - he fights as hard as he can, thrashing against Lucifer's will as violently as he did in Detroit, after he first let the Devil in. It's as effective as it was then - he's a grain of sand trying to hold back a tidal wave. He fights beyond his limits until he can't see or hear or feel anything anymore.
Sam gets control of his body again at a gas station. He looks around in confusion until he sees his hands are covered in blood. He can't remember what Lucifer did, nor does he want to, but he knows he can't stay where he is. He gets back into the car and drives back to Dean as quickly as he can.
Dean wakes up when Sam walks in and looks at him with a frown, "Where the hell did you go?" He sees Sam's hands, and adds, "What happened?"
Sam shakes his head and says, quietly, "I don't remember." He rushes past Dean to the bathroom to wash the blood off his hands.
"Well that can't be good." Dean mutters.
Sam washes his hands, and then gets in the shower because that just wasn't enough. He strains to remember what happened. Searches for glimpses of faces - anything that would explain the blood on his hands. He closes his eyes and searches inside himself, trying to at least figure out if Lucifer made him ingest any blood - maybe it wasn't human.
He hopes it wasn't human. He hopes it wasn't demon. He hopes it wasn't one and the same.
He can't feel any flickers of power and hopes that's because there aren't any. There are parts of his mind he can't touch (hidden from him)- because he buried his memories of Hell there and he's finally built up his own walls thick enough to keep them hidden. That's what he tells himself.
He almost believes it.
Lucifer doesn't appear again for two whole days. Far from making Sam feel better though, it makes him feel worse. He feels an odd pressure inside his head, and wonders if Lucifer is in there, waiting.
The walls in his mind are growing. He's starting to lose memories - not just bad ones, but good ones too. There's a smile he can almost remember, but he can't see the eyes that go with the smile, he can't remember the face, he can't remember the name.
They hunt a rakshasa, the next day, and just before Sam stabs it in the heart it locks eyes with him and says, "I know you." Sam stabs it and it hisses, "Daystar."
In the back of his mind, Sam hears Lucifer laughing.
They hunt a pair of ghosts in northern Montana - twin sisters. Dean is dousing the corpses in lighter fluid. The twins both appear in front of Sam, staring at him.
"Let us stay together."says the other.
"We know where we're going."
"We don't care - as long as you let us stay together."
Sam tries to tell them that he doesn't know where they're going, that for all he knows ghosts cease to exist when their bones are burned. He opens his mouth to tell them, and Lucifer says, "Why would I do that? My kingdom exists for your misery, not your benefit."
"Please." they say, as they go up in flame.
Dean walks over to Sam and snaps his Zippo shut. "What'd they say to you?"
Sam swallows, desperately hoping that his voice is his own, and says, "They just wanted to stay together."
Dean nods, and says "Well they got to cease existing together. That's gotta count for something." He turns on his heel and heads back to fill the graves with dirt.
Sam helps him, concentrating on the motion of the shovel, the scrape of the handle over an unhealed blister between his thumb and pointer finger. "Do you really think ghosts just...stop when we burn their bones?" Sam asks Dean.
Dean throws a shovelful of dirt back onto the grave and says, "I don't know Sam, and I don't really care, except..." He tosses another shovelful of dirt onto the grave, "it'd be nice if there was someway out, you know? Not up, or down, or trapped in the in-between, just...done." He finishes filling the grave and pats the underside of the shovel over the earth. "You know?"
Sam tries to think of something to say, but can't.
"The twins." Lucifer whispers. "They just got a warm, warm welcome."
Dean heads back towards the car. Sam drops his shovel, and bends to pick it up again. The soil looks like it's bleeding.
"There's no way out, Sam. No way to get off the tracks. Not for the twins, not for Dean, and not for you."
They get back to the house in Whitefish, and Sam storms into the bathroom, slams the door shut and glares into the mirror. "What do you want?" he whispers, "What are you doing?" He digs his thumb into his palm, pushing against the hardened scar-tissue there.
"For what?" Sam asks.
"Well, I can't just set up shop permanently, not yet. I told you - we're two halves of the same soul. We have to agree to be whole, or we'll just keep playing tug-of-war with one another. You've got home court advantage, of course, but I've got experience."
This time, when Lucifer laughs, it's with Sam's mouth.
Dean and Sam agree to meet with Crowley reluctantly. Crowley wants the Leviathans dealt with as much as they do.
They get to the empty warehouse right on time and wait for Crowley. They came prepared of course - holy water, salt ammo, and Ruby's blade at the ready. They expect Crowley to be duplicitous. What they don't expect is for him to appear and immediately fall to his knees in front of them.
"My lord." Crowley says, looking at the floor, "I had not heard of your release." He looks up at Sam slowly and smiles a frightened smile, "This is indeed a joyous day."
Sam looks at Crowley in horror, and sees Dean turn and stare at him out of the corner of his eye.
"Is this some kind of joke?" Dean snaps.
Crowley whips his head towards Dean angrily and snarls, "Shut your mouth before he kills us all."
"Sam?" Dean asks, staring at his brother.
Sam tries to tell Dean everything will be okay, but instead he hears himself say, "Reports of my imprisonment have been greatly exaggerated."
Dean staggers back, and his eyes widen with despair.
"Crowley," Lucifer says, "I hear you've been keeping my throne warm for me?"
Crowley gets to his feet, lifts his hands up, and takes a step back saying, "As acting regent only, sire. We all knew it was only a matter of time before your glorious return."
Lucifer nods, "Of course."
Sam screams his brother's name, and the scream rattles around inside his mind, useless.
Dean backs away from them, and darts out the door. Seconds later, the sound of a car peeling out onto the road echoes off the building.
Sam runs after Dean, but his legs aren't his own anymore, and he stays where he is - watching the self-proclaimed king of demons grovel at his feet.
Sam comes back home that night and finds Dean passed out on the couch. There are two empty whiskey bottles on the table. Sam goes to pull off Dean's boots, and something about the way Dean falls backwards is just...wrong. An empty pill bottle slips out of Dean's pocket and rolls off the couch and onto the floor.
Sam brings a shaky hand to Dean's ice-cold wrist and feels for a pulse.
He doesn't find one.
Sam's vision goes and he sinks to his knees by Dean's side. He says, "No, no, no, no..." over and over again and starts doing CPR without even really intending to - he's beyond rational thought, going through the right motions because it's a crisis and this is what he's supposed to do .
Dean doesn't respond. His heart doesn't start beating again, he doesn't take a breath by himself, he just lies there.
Sam feels Lucifer flow through his mind - his whispers skittering across his brain, as he says, "Suicides. They're all mine. All. Mine." the whisper gets louder, "Yes, it's all your fault...but it doesn't have to be like this. I'm an angel, you know. If I had my grace - "
Sam nods, furiously, as tears stream down his cheeks. The Enochian rolls off his tongue far too easily, and the floorboards beneath him turn to ash and fall away. The earth gapes open and Sam sees the Cage. He sees Michael and Adam and wonders if he's freeing them too. Lucifer's grace rushes up towards Sam, a living, breathing thing finally called home. It pours into him and he's filled with so much light and so much power that he can't see or hear anything anymore.
"There's no way out." he tells himself, "No way to get off the tracks."If that's true, Sam wonders, then why can't he see, or hear, or feel. If that's true, then where did everything go?
The Cage slams shut to the sound of Michael's screams and Adam's weeping.
Lucifer turns towards Dean and puts his hand on Dean's forehead. Dean's chest heaves - his back arching, and he gasps as he's torn back down to life.
When Dean opens his eyes, he's alone.