Cas|Sam
I hesitate to offer, because it is a sort of invasion, but honestly I highly doubt he's going to say anything actually helpful so...
Would you like me to show you? His dreams aren't pretty, but perhaps seeing the heart of his issues might help you help him heal all those old wounds or perhaps at least see that he's not the monster he believes himself to be.
I'm speaking, of course, to the dreams that are his and his alone and not the ones from the life the three of us share when we sleep.