How to deal with some one who is emotionally unstable and angry?

There this guy at my school . I am trying to be nice but he goes around telling people that I'm his girlfriend . We just met 3 weeks ago. He fallows me , constantly around me, he flips out when my guy friends are near me, he gets mad when I don't talk him etc.. . I am train in my Marshall arts today I almost had to use it . Because he grab my wrist because I got mad and walk away from him I told him also nicely to back up . Then he shouted at me as soon as the teachers broke it up with the help of the police . Then a few hours later he tried to talk to me again but I didn't really because one he made nervous and to it felt like I was dealing with some the fighters again because last year I got in to a mix match with them and people who work for MMA and combat. I do respect them but it was to hard to deal with . He also the same way. I can deal with but I am starting to feel really scared and unconformable because I don't like drama and I don't like feeling this way. I'm lost what do you think I should do . How can I avoid him nicely with out pissing him off. I appreciate the advice .