Of all the story directions that an overpowered main character can be involved with, the conspiracy plot is by far my personal favorite. An enemy you can't just smash. Problems you cannot just overcome with brute force or strength. Some of them are ironic, some are comedic, and some are serious. I enjoy them all. And I'm enjoying this one, too.
Also, I don't think he has a split personality,
@SaitoHimea . I think he did terrible things in the war and has been trying to move on, and that wizard had magic (and used words) that exploited his fears and insecurities. I'm sure his friends who died probably don't hold it against him at all that HE lived, why would they? If they were really his friends? But of course, he feels guilty, he blames himself, he feels like he should have saved them, so he imagines that they do hold it against him.
He probably, legitimately, has post-traumatic stress disorder. He needs help, and I imagine sending him to a school where he could make friends and not have to work very hard (by his standards) to succeed was his superior's idea of helping him adjust back into normal life. Unfortunately, their idea of helping adjust him back to normal has thrown him face-first into some fresh new hell.