I couldn't agree with you more on Castiel. I never saw him as a friend to Dean. In season four he was actively planning on destroying Sam and deliberately undermining the brotherly relationship. He flipped sides in season five and then continually berated Dean and Sam for starting the Apocalypse, without ever mentioning his part in starting things. I never forgave him for letting Sam out of the panic room and for not informing Dean that the voice mail had been changed. Plus he took the amulet on his useless search for God.

You are so right that he abandoned Dean during the year that Sam was soulless. Fandom was all over Sam and Bobby for keeping Sam's resurrection from Dean, but Cas never got called out on it. He continually used Dean and Sam in his war and did little to nothing to help them. He actively discouraged Dean from saving Sam's soul, which was unforgivable. Then he destroyed Sam's only protection as a way to slow Dean down. He killed thousands of people after his Purgatory power trip. I don't see how Dean could ever forgive him and yet there seems to be a consensus that he deserves redemption and a good hug.

As you can see, I really don't like the character of Castiel.