The moment that question is asked, it's as if all the air's been sucked out of Castiel. His shoulders slump, his head bows, but as much as he wishes it weren't the case, this is the state of things. It may be for the best that Sam knows, so that he doesn't take any sudden mood swings to heart.

"Crowley," he says with the most long-suffering sigh he can muster. "Demons are a maelstrom of feelings, it turns out." Not that he's that surprised by that revelation. They were once human, after all.

If Sam hadn't picked up on his misplaced feelings, then perhaps he's been paired off with someone less moody. Which is something Castiel can be glad for -- Sam deserves a break.