I think he had trauma and depression from his mother leaving, but he got misdiagnosed. Because of this he started to believe the diagnosis and truly lost most of his feelings. Later on, by faking them he slowly started to feel things for real. I think he was his own greatest enemy. Because he truly believed he couldn't feel, he also didn't (or didn't let himself). I think he wasn't actually very seriously mentally ill, except for depression, trauma, self hatred and so on.
Oh, and he saw his father, that wasn't really there for a while...maybe some schizophrenia or psychosis?