Get a little notebook to record any attempts he makes to contact you. It might be useful, if you have to make a police report.

I think you are very prudent to regard this guy with some measure of fear. About the safest thing you can do is try to avoid crossing paths with him. If you run into him, make yourself as boring as possible. But don't demonstrate fear. That can excite the "chase instinct." He's acting a little like a predator. You don't want to act like prey, but you certainly want to elude him as best you can. If he's telling you things "again and again," then you are giving him too much opportunity to talk. Don't keep explaining yourself to him. He knows perfectly well why the relationship ended. You'll never get through to him with reason and logic. He doesn't care about what is fair.

I'm not surprised to hear that he was abused by his father. That also tells you something about his mother - that she didn't protect him. So he's got plenty to be angry about. He is an extremely confused man, emotionally, and all you can do is separate yourself and move on with your life. And don't concern yourself with mutual friends who want to bring you two together again. This guy is dangerous, and now you see that. I'm glad you do.