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“Are you sure you’re up for this?” Dean asks for the umpteenth time, his eyes searching Sam’s for any sign of hesitation, though he doesn’t find any.

“I’m sure, Dean,” Sam promises him. “Come on. Please.”

“Just don’t wanna hurt you, sweetheart,” Dean says, trailing his hands down Sam’s bare thighs. Sam’s been seeming more and more… breakable, these days. He’s getting weaker and weaker, and the idea of doing something to accidentally make things worse is terrifying to Dean. He’d rather abstain from sex entirely than accidentally hurt Sam in some way, but Sam is adamant.

“You won’t hurt me,” Sam assures him. “I want you. Please, Dean.”

“Yeah, okay, Sammy,” Dean says. “I’ll take care of you, promise.”

Dean takes his time with prep, using more than enough lube and stretching Sam out, all the while checking to make sure Sam’s not in any pain or changing his mind. When Sam assures him he’s not, that he still wants this, Dean nods and retracts his fingers, kissing Sam slow and deep as he gradually pushes in. Sam sucks in a sharp breath at the feeling of Dean inside him, and for a moment, Dean panics, worried that he did something wrong or hurt Sam, but Sam quickly adjusts and eggs Dean on.

“Keep going,” he whispers, and Dean complies.

Dean sets a gentle pace, rolling his hips so sinfully slowly that it makes Sam’s toes curl in pleasure. A few times, Sam pleads for Dean to go faster, harder, but Dean never does, just continues to slowly thrust and pepper kisses across Sam’s face and neck. 

“You’re so beautiful, Sammy,” Dean whispers, rolling his hips just right to hit Sam’s prostate. He lowers his hand to Sam’s cock and slowly jacks him, all the while murmuring, “Come for me, baby brother.”

That’s all it takes to send Sam over the edge, his back arching and muscles contracting as he spills all over Dean’s hand and his chest. The feeling of Sam tightening and squeezing around him is enough to milk Dean’s own orgasm out of him, and he groans deep in his chest as he comes inside his brother. Once they’ve both come down from their highs, Dean pulls out gently and gathers Sam in his arms, stroking up and down his back and kissing the top of his head.

“You feelin’ okay?” he asks, and Sam nods weakly against his chest.

“Tired,” he murmurs. “But I still have research to do, about the… trials…” Sam yawns.

“Tomorrow,” Dean says. “For now, just get some sleep, okay, Sammy?”

Sam’s eyes fluttered closed, and he curls deeper into Dean’s chest. “You’ll stay with me?”

“Yeah, I’ll stay with you,” Dean promises. “I’m not going anywhere.”