The first time that they kiss is in a booth in some loud and overpriced bar. They're both drunk off their asses and being egged on by the cute blonde girls that Dean dragged back with him from the bar. Sam's not entirely sure, through the haze of beer and tequila, why they're kissing, but he thinks it has something to do with a dare.
All he knows is that he's shockingly aware of his brother; Dean's hand on the nape of Sam's neck, his thigh pressed tight against Sam's, his mouth, warm and wet and inviting Sam to dip in and taste. Sam forgets the bar, the girls, the reason they're doing this and concentrates on the flex of Dean's arm under Sam's hand, the way Dean kisses with total focus, the way Sam's stomach flips, alive with butterflies.
When they finally part, he's breathless and half hard and trying to remember why he's not supposed to kiss his brother. Dean's cheeks are flushed and his pupils are huge. He looks like temptation and sin. Sam's leaning in for another taste and Dean's moving to meet him when the girls giggle loudly. Sam had forgotten all about them. He glances at them and when he looks back at his brother, Dean's leaned back in his seat, beer at his lips, eyes avoiding Sam's. The moment is broken and Sam can't work out whether he's relieved or disappointed.
In the end, they get so drunk that the girls disappear off and he and Dean stagger back to the motel of the week, leaning on each other the whole way.
Sam wakes the next morning to a hangover of truly epic proportions and the vague memory of kissing someone he thinks he shouldn't have, but liking it. Dean's bad tempered and taciturn so Sam pops some Advil, drinks a pint of water and hopes that his stomach isn't going to rebel.
The second time has even less elegance than the first. Sam's too busy trying to get air into Dean's lungs to think about anything else. It's only when Dean finally inhales, chest rising and falling at last under Sam's hands that Sam remembers. He totally blames that sudden, unexpected sense memory, and the fear of having lost Dean for good for the way he presses his lips against Dean's once more. They share several breaths, before Dean's hand lands on Sam's shoulder. He's not pushing Sam away, but Sam lets his lips slide away from Dean's nonetheless. He pulls his brother into a sitting position and wraps his arms around him. The fear is fading and the inevitable draining of adrenaline leaves him shaky and clingy. Dean lets him hold on, doesn't complain, doesn't say anything. Sam turns his face into Dean's neck and if he presses his lips against the now strong pulse there, he figures he's entitled to.
The third time, they're hunting something that's hunting gay guys. They're in a club, trying to track the thing. The music is loud and Sam can feel the bass in his bones. Dean's somewhere in the crush of bodies closer to the dance floor. He looks surprisingly at ease, despite his bitching about having to go to this club. His jeans are black and way tighter than normal and the t-shirt is almost a size too small. Sam's eyes keep following his brother, even though he's supposed to be keeping an eye out for the thing they're hunting.
He sees it finally, standing against a wall. It doesn't see him though, because it only has eyes for one thing, Sam's brother. Sam wades through the mass of bodies, his size making the task a little easier. Dean's talking to some guy. Sam doesn't bother to say anything, just grabs Dean's arm and pulls him away and onto the floor. Dean protests, at least until Sam turns him so Dean's back is against Sam's chest. He leans down a little and tells Dean where to look to see their prey. His lips brush Dean's ear and it's not surprising because the music is so loud Dean wouldn't hear him otherwise. He feels the shiver run the entire length of Dean's spine and an answering one runs up Sam's. Sam keeps them moving, one hand on Dean's arm and one that somehow seems to have landed on Dean's hip.
They try and keep the thing in sight, but there are so many people that it's almost impossible. Dean finally grabs Sam's hand and drags him off the dance floor. He presses Sam against the wall a couple of dozen feet from the creature and plasters himself against Sam's front. Sam has no idea who moves first, because suddenly they're kissing again. It's supposed to be just for show, but Dean's got both eyes closed, one hand in the small of Sam's back and he's pressed tight against Sam. It takes next to no time for Sam to get hard and he doesn't care if Dean feels it, doesn't care that he likes this far, far too much. He understands now that he's been dreaming and wanting this ever since that first drunken kiss.
Dean pulls away, eyes wide and lips wet because Sam's been licking them. He's as breathless as Sam is and when Sam tries to pull him back in for another kiss, he just shakes his head slightly and says, 'Later," like he means it. He leads Sam out of the club, but instead of heading for the car, he takes him down an alley nearby. When they're almost out of sight of the street, he shoves Sam against the wall, fists a hand in his hair and yanks his head down. Sam goes oh-so willingly, no thoughts of sin or damnation could make him stop now.
He still senses when the creature enters the alley; the hairs on his arms stand up and the temperature around them starts to drop. The second it's in range, he pulls away, just as Dean's doing the same. The thing doesn't have a chance; silver bullets send it shrieking to it's knees as it bleeds thick black ichor, steaming and stinking of sulfur.
Sam has no clear idea of how they get back to the car, let alone the drive back to the motel. All he knows is that he can still feel the weight of Dean's body against his, the warmth of his mouth and the hard length of his cock as he ground against Sam in that alleyway.
The minute the motel room door shuts behind them, Dean's in Sam's space again. Sam gives as much as he takes, biting, licking, curling his hand around Dean's neck, using his thumb and the pressure of his mouth to tip Dean's head back until he can lick a strip up the vulnerable arch of Dean's throat. His brother's pulse is pounding, the vein in his neck jumping like a jackhammer and Sam's never felt more invincible or more exposed than he does right now. Dean's hands are tearing at their clothes, clearly desperate to get to skin, but Sam can't make himself leave Dean's mouth for long enough to help.
Dean pulls away one too many times and Sam doesn't bother to control the lust that slams through him. He picks Dean up and pins him against the wall. He shudders when Dean wraps a leg around Sam's waist and an arm around Sam's shoulders. He lets Sam support him, uses the leverage he's now got to roll his hips, grinding against Sam like he's in fucking heat and God, Sam can't stand it.
Dean's mouth tastes raw, and Sam catches a hint of coppery sweetness and he doesn't know which if them is bleeding, but he can't help chasing the taste anyway. He gets a hand down the back of Dean's jeans and cups his ass, helping him move against Sam, even though they're going to be sore from the friction later. It's so good, so fucking good that Sam doesn't care if he can't walk tomorrow.
When he comes, Dean moans into Sam's mouth and it makes something in Sam's gut clench. He can feel and hear and taste Dean's orgasm, and his brother sounds so wild, so out of control and lost in the sensation that Sam wants to bottle this moment and keep it forever, keep Dean forever.
Sam hasn't come like this, without a hand on him, or a warm body to fuck up into since he was a teenager but it doesn't matter, doesn't make this any less intense. His own orgasm stuns him when it happens, and he doesn't recognise the coughing, growling sound he makes that Dean eats out of his mouth.
Dean uncurls his leg from Sam's waist and Sam tries not to fall over. They stay against the wall for what feels like a long time, lips no longer touching, but close enough that they're still breathing each other in.
Sooner or later, they're going to have to move, but for now, Sam's content to stay right here, sharing Dean's air and feeling his brother's arms around him.