It started with a dream.
Sam was spread out over the hood of the Impala, the glossy black metal under his back still radiating heat into the rapidly cooling night. Sam recognized the Southwest in the desert air, charged with static and greedy for moisture as it rolled over his bare skin. It drew his attention to the wetness he felt between his legs.
Dean was sucking his cock.
The shock of it felt numbed, the sensation rolling through his body rather than slamming into him all at once. Dean was taking his time. Slow tender licks to the head; long sucking pulls around the shaft. Dean's lashes fluttered against his cheeks as he took Sam deep, his hands brushing along the inside of Sam's thighs before gently cupping and rolling his balls.
Sam had to look away then, had no choice, as he writhed there, caught between Dean and Dean's car. Trying and failing not to buck up into Dean's mouth. Feeling Dean's hair against his palms because he couldn't help himself, he had to touch him, had to feel him under his hands. It seemed to go on forever before Dean pulled off, his reddened lips pursed to press a teasingly chaste kiss to his slit.
Dean looked up at him, with that lop-sided grin that always drove Sam crazy.
"Make sure you tell me what you like best, Sammy."
Sam came all over Dean's face.
Sam woke gasping, the sheets twisted around his legs. The details of the dream refused to fade, and a cold sweat broke out over his skin. Sam hadn't had one like that in years, and it just figured that his subconscious would dredge those feelings back up at the worst possible time.
Two silent minutes were spent struggling to breathe quietly in the dark, heart pounding, a hand pressed tight to his mouth. Sam was skirting a fine line between the edge of panic on one side and hysterical laughter on the other. Because if he was completely honest with himself, what better vessel for Lucifer, the Lord of Temptation himself, than someone who wanted his own brother?
How was Sam supposed to deal with this? The end of the world was rushing towards them, the clash of Heaven and Hell all around them, and now he couldn't even control what was going on inside his own head.
The flannel shirt between Sam's cheek and the window flattened and slid, twisting his neck into an awkward position. Sam tried balling it back up tighter before he wedged it between his ear and the hot glass, determined to get some rest.
Dean was focused on the two-lane highway winding away in front of them, his fingers tapping lightly on the wheel. All will be revealed. Robert Plant wailed through the speakers, the volume at their usual compromise between Dean's Come on, I love this song, bitch and Sam's I'm trying to sleep, asswipe. Sam shifted stiffly in his seat as the familiar riffs vibrated in his bones. Like thoughts inside a dream. Even Led Zeppelin seemed to be calling him out for wanting to fuck Dean. Figures.
Dean gave him a steady, lingering glance out of the corner of his eye, and Sam knew that he'd been made. Neither of them had been getting much sleep since they lost Adam to Michael, but Sam had been fidgeting all morning, giving away the fact that something else was bothering him.
Dean rolled his shoulders, dropping one hand onto his right thigh and leaning the other shoulder against the door. It angled his whole body slightly towards Sam, a casual position that was classic Dean-speak for Well, I'm listening.
But Sam's eyes were drawn to Dean's thigh, his fingers splayed out on the thin, weathered denim. Dean's thumb was probably pressed to the inseam and Sam wanted to slide his own hand right there, follow the seam up Dean's thigh and the words road head lit up in Sam's mind like a neon sign- Dean gasping and cursing, one hand fisting in Sam's hair while the other clenched white-knuckled on the wheel, keeping them on the road while Sam blew him, sloppy and frantic and fucking perfect- before he could stop himself from imagining it.
Tension was beginning to build in Dean's body as the seconds ticked by, and Sam couldn't blame him. They had a pretty nasty track record for this; for the times when Sam didn't immediately come clean when Dean gave him the chance to talk it out. And Sam realized that if Dean got suspicious, if he really started watching Sam, Dean would get to the bottom of this.
Knowing Dean, not even the Apocalypse would be able to distract him. And if given the chance, Sam would rather take this one to the grave.
When Dean cut his eyes over again, Sam gave him the grumpiest look he could manage, rolling his eyes and reaching over to turn down the volume. After a long moment, Dean seemed satisfied, and turned it back up.
It was a new dream.
Dean had Sam by the wrist, reaching for Sam's face. Sam saw his lips move, a soundless Sammy that somehow reached him anyway. Sam knew without looking that the grip on his ankle was Lucifer.
Neither of them were going to let go of him. It was up to Sam.
I love you. Sam twisted his wrist, slipping free. I love you, Dean.
Sam spent what felt like the most important five minutes of his life squeezing a promise out of Dean.
Sitting shotgun as the Impala slid through the darkness, reading flashes of Dean's face as streetlights passed overhead, trying to make Dean understand without having to say it.
He'd like to think that telling Dean to find Lisa wasn't selfish, but he knew that wasn't true. It was the only way he could do this. Because if he thought for a second that Dean wouldn't be safe in the aftermath, Sam knew he wouldn't have the spine to go through with it.
Sam needed that promise more than he needed anything else in those last few hours of his life.
And in their final quiet moments, with Cas passed out in the back and just Dean there to hear it, Sam could have told him. Could have told him his last secret, the only thing about him that Dean didn't know.
Sam watched Dean for a while, taking him in. Memorizing as many details as he could of his brother, just like that, in the driver's seat. The two of them, one more time, driving into the unknown.
Sam made his peace with how he felt, then buried it as deep as it would go.
Dean was never going to know.
Maybe if things had been different. Maybe if there was even the smallest chance that Sam could make it out alive, he could have told him. But as it was, he wasn't going to drop a bomb like that on Dean and then disappear forever. Dean didn't need that shit on top of everything else.
Better for him to remember Sam exactly as he was; remember them exactly as they've always been.
And if Sam did make it out of Hell alive, well...
Sam had done far worse things than loving Dean too much. Dean had always found a way to forgive him.