How do I get a guy to leave me alone!?

Sorry if it’s long… please read! So this guy at school, I used to talk to him occassionally because I sat next to him during my English class. I moved to Arizona for 5 months, for the winter, and just recently came back. I don’t talk to him anymore. I guess you could say I’m getting bad vibes from him. Whenever I’m near him, I feel scared, like I need to run, and also like I need to be comforted? Whenever I have a class with him, I get really nervous and that someone-just-walked-over-your-grave-feeling. He ALWAYS stares at me. It scares me! Whenever I’m in the hall, or the class has free time to walk around etc., he follows me around and kind of corners me against walls. He’s never more than 3 feet away from me. If I move, he follows me. I once tested it by walking all the way across the room, and he followed me and kind of circled me. He doesn’t even say anything, just stares at me. My friend noticed, too, and she’ll stand between us, but that only makes him step closer. She told him today to stay away from me, and he kind of shrugged it off, like she was just in his way. I’m really scared. help? I can’t tell him myself to leave me alone, I feel guilty even thinking about it, though I don’t know why. I also freeze up and freak out.