im sorry OP, hope it worked out okay

Time for a public scene. They can't do this shit if it's not secretive. Throw a fit. "I ONLY SAID YES BECAUSE I WAS SCARED OF WHAT PSYCHO CRAP YOU'D PULL THIS TIME!" Get in your head a list of examples and make a scene in front of your friends, his friends, etc. State specific occurrences. Then...everyone will know. And he knows they know and that you will air his dirty laundry in public. If you go to a school, tell the security office, counselors, etc. about your concerns. But be loud. Be visible. Make it clear that any shit he does, EVERYONE will know about. And if he tries to retaliate? TELL THEM ALL AGAIN. Loudly. In public. If it's on the phone, hit the speaker button and get into public as quickly as you can. Get another male with a deep, threatening voice to deliver a few threats on your phone on your behalf. Take away his power by making every stunt he pulls public knowledge. And then each time, ask about his former girlfriends. That should help make those around him start thinking. And for God's sake...tell your parents and his parents precisely what is happening.