Of course, we all love the idea that our past boyfriends have just been pining away for us ever since. And sometimes, maybe, they do. But it's also possible that someone like him used his unrequited "passion" for you as an excuse not to let anyone else actually get close and make a life with him (you did say he'd never married, right?).
Or maybe he's just a depressed alcoholic and those high school times with you were the last times he can remember being happy.
Still, it seems like you should hear him out at least.
