I think your character is repressing a bunch, especially since he won't get close to anyone. You have to find the button that's going to unlock all of his craziness. What's sacred to him? Find it, and poke it with a stick, and then maybe laugh.

If your female MC's sister is spunky, she's probably going to try to press all his buttons for you. I'd let her happen to find out about this dead best friend, then take him to a seance and see what happens. Even if the seance is crap, he'll probably react, right?