After 11 days of losing Dean each day, Sam stops crying himself to sleep, hoping that the day will in fact repeat and give him more time to figure this out and to see his brother alive again.
23 days later, he's followed every lead and worked all the possible angles and they're still stuck in Groundhog Day. It's the first time he laughs at the way Dean dies (c'mon, nobody can suck that bad in archery). When Dean stops breathing, his blood all over Sam's hands and shirt, eyes wide and confused, Sam's hysterical and can't stop cackling. He cries again that night.
After that day, the massive guilt makes him hold Dean every time he can, trying to find the words that comfort Dean the best. Dean knows Sam's theory about Groundhog Day, but instead of the encouraging phrases like "I'll see you tomorrow", or "it's gonna be okay", Dean responds best to simple "I love you".
45 days since the never-ending Tuesdays started, Sam lets himself wonder what if he kissed Dean. There'd be no long-lasting repercussions, because Dean would reset and Sam would have the one thing he's never really allowed himself to think about. The knowledge of how his brother kisses, the give of his lips under Sam's, the roughness of his stubble. He could try and really know how Dean would react. Would know if it's anger, disappointment, submission. Or maybe a dismissal or a cruel laugh. Or if Dean kissed him back. He could even do more if Dean let him. Or even if he didn't. Sam kisses Dean after he's gone.
13 days later Sam kisses Dean goodbye when he's still drawing breath and Dean clenches his fist in Sam's jacket in response. Dean's eyes widen a bit before the light in them dies. It's the farthest--and earliest--Sam lets himself go. He doesn't want to know Dean's real response on a never-ending Tuesday, not when Dean will rock out to Asia when Sam wakes up, give him a big smile, and Sam has to live with whatever Dean said. He can't risk it, because if Dean rejects him, Sam has nowhere to run with his broken heart.
Wednesday finally comes and Sam has prepared for every possible reaction Dean could have. He doesn't get a chance to kiss him before the day's over and Dean dies.
Sam loses himself for a while, but he gets back to that Wednesday. Dean's back to himself, brushing his teeth of all things, and he's so beautiful.
Sam jumps from the bed. He hugs Dean and then kisses him.