This guy is creeping me out. Help!?

he's in 8th grade and I'm in high school. He sits by me every single day in the morning and the afternoon even when there are other empty seats. But he never talks to me. And he stares at me the entire time or he stares at my legs, I look at him and he won't stop staring at me. I started to put my backpack on te other side of the seat so he couldn't sit there but now he's askin me if he can sit by me. And I don't wanna be mean and say no so I just move my backpack and let him sit there. & sometimes I just pretend I can't hear him Cuz I have headphones in and then he taps me! I try to scooch away from him and he scootches so close I can barely move. and he pretends he's grabbing his phone from his pocket but he's really like sliding his hand by my ***!!!! This has been happening for a month