"You got any kind of idea what kind of sight that is to walk in on?" Sam shook his bangs out of his eyes and pressed a kiss to Dean's shoulder.
He'd thought he was going crazy when he found Dean in bed with an older version of himself, found them together and kissing, but Older Sam had taken enough time out to explain that yes, he really was from the future, and no, he didn't know how he got there, and yes, they should definitely worry about getting him back to his own time except after because he was really hard and he really, really wanted to fuck Dean, and did Sam mind?
No, Sam didn't mind, as long as he wasn't banished from the room. So here he was, crouched beside Dean, watching his brother ride Older Sam slowly, thighs trembling a little from the strain, head thrown back and throat exposed in one glorious line he wanted to lick, so he did. Hey, active participant!
"God, Dean," Older Sam moaned, staring at Dean like he was, god, everything good in the universe. "I missed you. Missed this, so much."
"What, you don't do this with me in the future?" Dean panted softly as he lowered himself back down again. He was taking it so slow, it had to be driving the both of them crazy. "Future me turn into some freaky monk or somethin'? Because I've never been able to resist you and your monster cock."
Sam snorted and stroked his own dick. It was hotter than he would have thought, watching the two of them. He was so hard, and aching already, Jesus, but he didn't want to come yet. Not when he had such a good show.
"Less a matter of you saying no, more that you aren't there." Older Sam's hips shoved off the bed, pushing his cock deeper into Dean like he just couldn't help himself. Dean opened his mouth like he wanted to ask more questions, and Older Sam gripped his hips tighter. "We can talk after, if you don't mind-" he thrust up again, and Dean let out a choked whine and nodded.
"Okay, okay, fuck," Dean picked up the pace, moving faster now like he couldn't hold back anymore. "Sammy!"
"Which one of us are you moaning for, Dean?" Sam couldn't keep his hands off of Dean any longer. Abandoning his own dick for the moment, he slid them all over Dean, pinching a nipple just to hear him cry out, letting his other hand go down, between his cheeks to gently touch the place where he was split wide open for Older Sam.
"So wide open right now aren't you," he purred into Dean's ear, grinning at the wild noise he made. Beneath him, Older Sam wasn't unaffected, letting out a groan. "Split open on his dick and loving it, so hungry for cock. God, wouldn't you love it if I could get in there as well, stuff you full of two cocks, would you like that? So full of Sammy you can't think straight?"
Dean shoved into his hand when he brushed a finger over the head of his dick. He was so hard, it looked painful. He wasn't touching it though, wasn't fucking into his fist; both his hands were on Older Sam's chest, still fucking himself on that dick, even though his legs had to be hurting.
"Know you love being fucked, love being full." Carefully, carefully Sam pushed his finger into Dean alongside Older Sam's dick. God, he was already so stretched open. "You take it all, everything, fingers, tongue, cock. Such a good boy, maybe later we really can try to get two dicks into you when you're still open and sloppy with a load of come."
Sam wrapped his hand around Dean's dick and pumped once, and Dean came, muttering obscenities and, "Sam, Sammy, Sam," moaning for both of them, maybe just one of them, who knew.
Dean clenched tight around Sam's finger and Older Sam's dick, and that was it for Older Sam, too. He gripped Dean's head in his huge hands, pulling him down for a frantic, messy kiss as he filled Dean with his come (no condom, idiots, Sam hoped his future self didn't have any freaky diseases.)
Sam's own dick was practically threatening to disown him if he didn't touch it, and he jacked himself frantically, three, four strokes and his come streaked Dean's side and Older Sam's leg.
Silence as they all came down. Older Sam wasn't kissing Dean anymore, just clinging to him, holding him tight to his chest. "Thank you. Dean, god, Dean, thank you," he whispered, voice shaking, hand stroking over Dean's back tenderly.
Sam felt oddly like he was intruding on something by watching, seeing this older version of himself so open and emotional, thanking Dean with what sounded like tears in his voice, so he climbed off the bed and went to the bathroom for a towel to clean them all off.
When he came back, Dean was sitting beside Older Sam. They all wiped themselves off best they could (though Dean would need a shower, he had come in his ass and all, and that couldn't be too nice), then Older Sam looked back and forth between them and said somberly, "We need to talk."
Dean didn't even crack a joke, just put a hand on Older Sam’s shoulder and left it there as they shared a long look, then it was one big scramble for clothing, getting settled on the clean bed, and Older Sam trying to explain how to keep them from years of misery.