HELP ME!!!!

Ok, im 13 and there is this guy and we have a class together during school. He comes up behind me and he says in my ear "hi, emily." He also sits by me during class most days even though he isn't supposed to. He also one time grabed my thigh and i just walked away to my friends. And he has a gf!!!! It also doesnt help my locker is by his.... I just dont know what to do!!! I dont even know if I like him. What should I do??