Is it sexual harassment?

You absolutely should tell a teacher. It's not OK for him to touch you inappropriately even once, but he has been doing it repeatedly despite you telling him not to. Tell the teacher exactly what you said here, and be prepared to give specific examples of his behavior. Telling your classmates isn't going to help, and it isn't their responsibility. They're probably intimidated by this creep too. If you aren't comfortable approaching this particular teacher, talk to a different teacher, counselor, or whatever, and they are required to handle it. He/she should not ask your classmates because this is a personal matter between you & him. But yes, he/she or someone will have to tell him what you said, otherwise they're not really handling it. So what, too bad for him, he's the one doing something wrong, not you. Don't worry about the teacher thinking he's being bullied - HE is bullying YOU. By speaking up, you may very well be also preventing him from doing this to anyone else.