Skeletons
Relationships break slowly. He's learnt that much by now.
They don't fall apart all at once. They fall apart piece by piece, like a tree loses one leaf after another until there's nothing left but a bare black skeleton against the pale blue sky.
The little things come first, little rituals like the quick goodbye kiss before he leaves to work, or the Sunday mornings at Sally's. And then, gradually, everything starts breaking down, until there's just nothing left worth fighting for. Until they're holding on to nothing more than the skeleton of what used to be their relationship.
He'd tried to stop it, he really had. But when he'd managed to gather some of the leafs scattered across the floor, the wind had already blown down dozens of other leafs. And so, eventually, he'd stopped trying.
He'd started hoping that maybe, maybe, the skeleton of their relationship – their love – would be enough to hold on to. That if they just managed to hold on a little more, spring would come again and new leafs would grow and everything would be alright again.
But bones can break. And so they did.
They started crumbling, falling apart, just like everything else, and then, there was nothing left. The tree died, its skeleton turned to dust, rotting on the ground with all its brown and crumbled leafs.
Now they're here. And while he's frantically trying to rebuild the skeleton, to make it stand again, to save the tree, to save their relationship, Dean's just standing there, looking at him.
For a brief, bittersweet moment they are frozen like this, frozen in the last moment of their dying relationship, frozen among the remnants of what they used to be, and then he realizes that there's no point in holding on anymore, because he's the only one holding on, and so he breathes out one fateful word.
"Go."
Dean does, but he turns around one last time before he leaves the apartment. "Why do you still love me?", he asks.
Cas smiles sadly. "I don't know. I genuinely don't know."
He takes a deep breath before he asks his last question. "Why did you stop?"