Sometimes Castiel just can't feel anything. He wants to, he really does, but he just can't. This is when he turns to the drugs and the women, when he just can't feel anything anymore. This feeling becomes more and more regular. So regular, in fact, that Castiel sometimes doesn't believe he's even himself anymore.
Sometimes Dean stares at him a little weirdly, almost like he sees it too, but that's impossible, he doesn't talk to Dean enough anymore for him to choose what's 'normal' or not. He misses Dean, but he's almost sure that Dean isn't the same anymore either. He guesses that that's just what the apocalypse will do to you. They might all die anyway, It's hard to stay the same with those odds .
He misses everyone. The angels, Sam, the old Dean, Bobby, Garth, Kevin. He could go on and on, but it wouldn't do anyone any good, especially him. So, sometimes he's so sad he can't seem to go on, and sometimes he can't feel a damn thing, but he knows which one is worse. At least when you are sad you have something to hold on to, something to ground you, but when you can't feel anything, you just are there.
Dean stopped staring at him. Maybe it's for the best, he didn't like the judging eyes anyway. Or at least that's what he tells himself. They probably weren't even judging, just concerned. He kind of hates Dean for that too.
With the end nearing, Castiel fears that it's better to feel nothing at all.