Dean can forgive Castiel after Cas crashes Sam’s hell wall which drove Sam insane. He can forgive Castiel after Cas lets the Leviathan loose on the world.
But Dean cannot forgive Castiel ignoring him. Because to Dean, Castiel is everything and when Castiel disappeared on…
Also: Dean forgave Sam after he left the family behind for Stanford for several years, for not getting along with Dad up until his dying day, for the whole RUBY fiasco, for tripping the apocalypse, for acting like a dick when he didn’t have a soul, for not searching for him in Purgatory, and for a thousand other mini-dramas that happen at least once every few episodes. :) The only thing Dean can’t accept is being without Sam. I think Dean hated when Cas disappeared because he has precious few dear ones. Although… He tried to move on when he thought Cas was dead, bloody coat and internalized sadness aside. He simply cannot move on or peacefully accept life without Sam, and when he fulfilled his promise to try with Lisa and Ben, it was a life full of alcoholism and nightmares and withdrawal. So. :)
