A/N: This is an incredibly silly thing I wrote for comment_fic for the prompt 'when an angel takes a mate'.
The whole thing began about three months after Dean and Castiel started fucking.
Well, it wasn't just fucking, but Dean chose to call it that in his head so he could avoid thinking about the fact that he was sorta in love with a fucking angel of the Lord.
Anyway, whatever he called their relationship, it was pretty normal for those three months. Or as normal as possible when one partner had the ability to appear out of nowhere when he wanted to get laid and had trouble keeping his wings fully sheathed when he came. Castiel had been among humans long enough to realize when it was a good time for sex though and once they'd gotten over the weird transition from kinda friends to definitely lovers, it was easy enough to maneuver finding privacy and not letting Sam become the third wheel.
All in all, Dean was pretty damned happy with the arrangement. Regular sex with a partner he actually knew and didn't make him feel dumb for sometimes wanting to just lie together without the actual sex part. Who quietly accepted Dean's whispered endearments with a soft smile and returned them with such a serious expression that Dean really believed him.
Then it all got a little weird.
At first, it wasn't so bad. Just that after they'd had sex one night and Dean was drowsing lazily, he felt Castiel's gaze heavy on his face.
He dragged his eyes open and startled at the heated look in Castiel's eyes.
"Dude, are you ok?"
"I'd like to do that again," Castiel said, voice slightly strangled.
"Um…we just got done," Dean said.
"I'm ready again," Castiel assured him. A glance down confirmed this statement and yeah, Dean was tired and it was weird, but also hot that Castiel wanted him again already, so he thought why not?
When Cas was ready again a second time, Dean told him to shove off. Which he did, disappearing in a flutter of wings, presumably to take care of things himself somewhere. Dean just rolled his eyes and fell asleep.
The next day, Castiel apologized for leaving and life went on.
Except the whole two and three times a night thing kept happening. On the one hand, Dean was absolutely in favor of more sex. But on the other, his ass hurt. When he told Castiel this, Cas accepted it with good grace and told Dean they could relax for the night. But the way he kept looking at Dean, his gaze hot and possessive and the way he kept shifting in discomfort bothered Dean. It was almost like…well, it was like Castiel was in pain. Like his desire for Dean was actually hurting him and that wouldn't do.
"Just come on," Dean said finally. He'd barely gotten the words out before Cas was on him, fingers tearing at the buttons of his shirt.
Even that didn't really alarm Dean.
It was the whole ordeal at the laundry mat.
Sam and Dean were doing their normal bi-weekly laundry duty when Castiel exploded into the room with absolutely no finesse. A bunch of papers tacked to a community notice board rained down on the ground and the hair was lifted off the brothers' foreheads. If anyone else had been in the room, they'd have noticed the entrance for sure and that wasn't like Castiel.
"Cas?" Dean asked in concern. Especially when he saw the strange almost crazed look in Castiel's eyes. Cas stalked forward, zeroed in on Dean as if he were the only thing in Castiel's existence.
"Are you ok?" he spluttered, a little afraid, but also turned on by that powerful focus.
"Dean," Cas whispered, voice little more than a wrecked growl. Dean heard Sam say something, probably a protest, but Dean ignored him. He grabbed Castiel's hand because he got the message in what Castiel couldn't say. For some reason, Cas needed him and needed him now. He was barely holding on and Dean didn't want to see what happened if Castiel didn't get what he needed as soon as possible. Somehow Castiel managed to get them back to the right motel room before he lost it completely.
When it was over and Castiel was calm once more, Dean decided it was time for a mini-intervention.
"So…are you going to tell me what the hell that was about?" he asked, keeping his voice fairly neutral as he rubbed Castiel's back. He frowned when Cas tensed under his hand.
"I'm sorry, Dean," Castiel said and he hauled himself up, swinging his legs over the side of the bed and facing away from Dean.
"Sorry for what?" Dean asked anxiously. He really didn't like that note of self-loathing in Castiel's tone. "What the matter?"
"It's the...I didn't think it was real," Castiel said.
"Didn't think what was real?" Dean tried not to panic or imagine that Castiel was sick or possessed or some disturbing combination of the two.
"When angels take a mate," Castiel said, his voice soft and full of something Dean couldn't place. "When it's binding, I've read there can be...side effects."
"Binding," Dean said blankly. "Meaning...?"
"When the...when the two partners have given themselves to each other fully," Castiel explained and he sounded fairly calm for someone explaining to their boyfriend that they were basically married in angelic terms.
"Um...so...side effects?" Dean squeaked, then coughed and cleared his throat. "You mean this whole pon farr thing?"
Castiel tilted his head back enough for Dean to see his eyes, which were confused. "I don't recognize that term."
"The..." Dean twirled one finger as if that were the proper sign for 'lots and lots of fucking.' "The desperate sex thing," he finally said.
"Oh yes," Castiel agreed. "Yes, pon farr."
Oh god, only Winchesters. Dean swallowed hard and scratched the side of his head.
"Well...is it permanent?"
He could get used to it, he thought. As long as Castiel gave him time to eat and sleep occasionally, maybe tried to find a way to keep calm while Dean was hunting.
"No, according to the writings, it fades after what would equate to several Earth months," Castiel said and he sounded very troubled. "I'm so sorry, Dean, I should be able to control myself, but then I...I think about you or I see you and I just..." His voice dropped to a whisper. "I have to have you."
"Dude, that's..." Dean was torn between expounding all the reasons why that was so hot it hurt and trying to comfort Castiel. In the end, he decided to let his actions do the talking. He climbed behind Castiel, legs on either side of his body and wrapped his arms around his chest.
"It's not your fault," Dean said, lips against Cas' ear. "I can handle it. I mean, if we're going to do this 'binding' thing, we might as well have the honeymoon."
Something about his words or their position or both obviously hit the spot because Dean suddenly found himself flat on his back and looking up at Castiel's dark needy eyes.
"You mean that," he murmured more to himself than anything.
Dean wasn't sure if he was required to talk, but he did anyway.
"Yeah, sure, of course," he said, hands cupping Castiel's face. Castiel tilted his head into Dean's palm and Dean felt him begin to tremble.
"We're going to have sex again, aren't we?" Dean asked.
"Yes, please," Castiel breathed.
Dean grinned. Oh yeah, he could totally handle a little angelic pon farr.