It's pretty obvious that this is just how Dean feels. Well written. I just wish Sam,(or even Castiel) could make him see that that darkness is in all of us, and that he should be proud of the fact that he just SURVIVED! Whole, and sane, and able to still feel guilt and pain and remorse. And Compassion. It was his darkness that made him strong enough to hold onto himself. (Just as I believe John did. Two men who had learned to be hard and unfeeling when they had to be, to save themselves and the world. ) Has Dean ever thought about what John had to do to survive for 100 years? Not before, certainly, but now? Now that he understands what really happened to his father? Would he hate his father for it, as he hates himself right now? Would he rather have been turned, become truly unfeeling as a Demon? I think not, despite the pain he lives with now. I hope he can finally learn, in time, to accept that he is just a man. A strong, good man. If he can't, I don't think he'll be ready to save his brother when Sam really needs him, at the end. And that is what he was born to do.

Very dark and lonely version of Dean.

I mean that in a good way.