If you asked Samuel Winchester when things had gone awry in his life, he would tell you that they had always been fucked up. Those were his only memories, all that he had grown up with. He couldn't remember his mother's soft crooning, his father's weary shuffle and mumbled whispers of comfort, or the fiercely protective green gaze of his older brother over the rail of his crib. Yet all of these things unknowingly stayed in Sam's life, bringing automatic and unconscious comfort to him even in the middle of asscrack nowhere.
Dean's gaze was still just as piercing and protective, but now there was more in those fierce depths; respect, sympathy, love, and something darker that made Sam's stomach leap to his throat and his cheeks to flush hot.
Coming back to dingy motel rooms after a hunt only made the weight of the brother's weariness that much more prominent. Sam would collapse onto his bed immediately seeking sleep, but it was only after listening to Dean's weary shuffle back to his own bed and the whispered "Night Sammy," that he could fall into a dreamless sleep.
The last of Sam's unconscious comfort triggers happened far less frequently than the other two, but it was the one that was by far the most effective. The nightmares still came, not as often, but no less disturbing, and would always manage to make the youngest Winchester writhe and moan, bathed in a panicked sweat and trapped in a world he could never seem to escape. Then out of the darkness would come a sound, starting quietly, almost like an illusion, but it continued to grow louder and stronger until the demon wrapped around Sam's mind hissed angrily and receded back into the darkness muttering curses. That song did not stop then though, it continued slowly and soothingly, holding Sam entranced in its velvety croons like a pair of strong, protective arms. When the voice sang that song, familiar, yet different enough that his mind was unable to pinpoint it, Sam would sleep better than on any other night.
Dean watched his little brother sleep soundly and dreamlessly in his arms and a picture of a chubby-cheeked, 6 month old would flash through his mind. Dean remembered the soft lullaby his mother sang, the way his father walked down the hall grumbling even though he smiled as he shushed his youngest son, and most of all, the promise he made himself to protect that screaming, red-faced thing that was his brother. Dean remembered, and he would ensure that Sam did too, whether he knew it or not.