For Dean, when it comes to having Sam back with his soul, it's the little things that count.
For instance; when Sam's hand inch towards the radio dial in a fashion he believes to be sneaky when Hair of a Dog belts its way out of his beloved Impala's speakers and Dean has to slap Sam's hand away with a smile spread wide across his face while Sam tries not to pout too much, or when Sam spends at least half the morning in the bathroom while Dean pretends to bitch on the other side of the door when in fact he feels about ready to burst out of his skin due to the pure joy. The joy that he's got his Sammy back.
He doesn't show it though, he masks it with half hearted glares and brotherly banter that borders on careless and rude. Sam just takes it with an open mind and heart, too, because for him, nothing has changed. Dean plans to keep it that way.
It doesn't help when Sam begins to remember, though…especially not when Cas tells him the truth.
Bless Cas' heart, or maybe it's his Grace, Dean's not really sure, but maybe it's for the best if Sam does know. Maybe this way, Dean can make sure that it's not on accident that Sam begins to tear down that wall put up so hastily and thoughtlessly inside his head. Dean just knows there will never be a time where he isn't genuinely scared for the well being and sanity of his family in his life.
Sam brushes it off though, because he's Sam. Because he's been through Hell and back, even if he doesn't remember it completely. Sam puts his blind faith into Dean's hands once again and Dean hit the ground running with it. That's all Dean can do, really…run. He runs through his life, runs into battles swinging widly, runs through the dark with his eyes closed and arms spread wide. Dean never stops, never falters, he just goes.
It's only when Sam hits the ground, mouth ripped open with a silent scream, that Dean takes a moment to stop.
Stop pretending that things will be okay now.
Stop trying to outrun the past.
It's as if Sam's wall is his own and he's hit it at full force.
And Dean doesn't know if he'll be able to get up again without Sam by his side