Don't talk to him. It's not a good idea for you to have any more contact with him whatsoever.
If you can, get a friend who knows both of you to sit him down and tell him to back off - to say he's scaring you, he's worrying you, and you turned to them in order to try to get him to understand. If he gets violent at that person or at you for contacting that person, that's when it's a good idea to threaten him with legal action (violence is a definite no, even if he means well) - via a nice formal letter which hopefully goes through his parents !!
Usually a formal, distant threat will make him realise that you mean business (even if you never end up going to the cops). In fact, the police can't do anything unless he makes a physical attempt to harm you or sits outside your house for three days without moving or something.