Dean ignores it for as long as he can, tries to give Sam his space, give him his privacy - as much privacy as he can, anyway, with Sam in the other bed, sound of his hitched breaths and the sight of his shoulders shaking under the covers in the dark breaking him apart, making him ache somewhere deep down next to his bones, under his ribs between his lungs.
He wants to crawl inside him and soothe the hurt, wrap Sam’s heart up so tight nothing can ever wound it again but he can’t. He doesn’t know how. Sam is grieving for Jessica and for the life he built for himself and for all the dreams that went up in flames that night and Dean doesn’t know how to make it better and it hurts so bad he can’t breathe, sometimes.
He leaves Sam alone as long as he can, makes it four nights before he just can’t take it anymore, can’t listen to Sam cry himself to sleep another night without breaking down himself. He slips under the covers and wraps his arms around Sam from behind and pulls him close, doesn’t say a word when Sam’s sob breaks the silence, holds him tighter when Sam grabs his hand and holds on like Dean’s the only thing keeping him from falling.
It takes weeks for Sam to stop crying, but Dean doesn’t mind. When the nightmares wake him up in the middle of the night Dean is there, carding his fingers through Sam’s hair and rubbing his back and whispering to him in the dark, soothing him back to sleep like he used to when Sam was little and Sam lets him, curls up and tucks his face into Dean’s chest and falls asleep again.
Dean doesn’t know what else he can do, hopes that this is enough. Enough to remind Sam that he’s not alone, that no matter how dark things get, Dean will never leave him. He can’t take this from Sam, can’t cut it out or make him forget or protect him from it, but he can do this, and when Sam takes a shaky breath and presses a kiss to his collarbone and whispers thanks, Dean, he thinks it’s enough.