Dean and Castiel weren’t supposed to happen, but they did. They are improbable and undeniable. As improbable as Dean being dragged out of Hell by something he never believed in, as improbable as Dean dragging an angel down from Heaven. They were reluctant - Dean to believe, and Castiel to doubt - but they were bound to come together. Maybe from when Castiel first laid his hand on Dean in Hell, or maybe just from when Dean first challenged Castiel and Cas first saw right through Dean. They haven’t stopped getting under each other’s skin since. They struggle to understand each other, they trust each other when they shouldn’t, they save each other and nearly (or actually) destroy each other. Dean blew apart Castiel’s existence, and Cas broke Dean to pieces. But Dean wants Cas back anyways, and Cas’ll go with him. They can’t deny what they mean to each other. And it’s something they can share with just a look.