I need help!!!!! 10 points for best answer!!?

Okay so I am twelve and school is about to end. But we already got our schedules for next year. Well there is this guy in my class who is really big and strong....but ugly! He likes me a lot. Well in the middle of the year when I walked by he squeezed my *** or he would pretend to fall into me and rub my boobs. Well it has gotten really extreme. Once when I went into the restrooms he followed me....(and it was the girls) and I didn't know so I was peeing and then changing my tampon and he peeked over the edge of the stall. Then he crawled under the stall and taped me to the toilet. Then he started finger my vagina and shoving things up there!!! It hurt so bad!!!! Now every time he sees me he smiles!!! I'm scared...but I don't want to tell a teacher or my foster parents (my real parents got murdered) please I need help I'm super scared..plus the guy is in my class next year!!!!!! :(