I definitely understand your confusion. I also had great parents, great family, wasn't bullied. I've had it better than most people. There isn't any one cause that I can point at and say that that's the reason.

But my best guess for a cause would be some sort of abandonment issue. I've lived in a military town my whole life, but am not a military kid. So every year I lost friends, never to really hear from them again. I eventually gave up on making friends just to have them move. I really don't know how that led to it, frustration I guess?