Dean is happier than Cas has ever seen him. He worries about Sam, but that's going to be true no matter what else is going on. He also worries about Cas because Cas is spending more and more time as a human. He wants to make sure Cas is okay, but also express that Cas is actually taking advantage of the chance they have in this place to have a real life rather than some life lived between bouts of saving the world and/or dying.

Dean looks surprised then scowls a little at Cas. "Dude, I don't need to hear about your angel junk." He hesitates a little. "Lucy doesn't seem like a one week a month girl," As far as sex goes, he means." Plus she's human. I didn't know if like angel sex would kill her. Or if you even got your rocks off when you were an angel. It's not like the other angels are running around hooking up." After all, Anna didn't have her grace when he slept with her.