What does it mean when a guy doesnt like you but masturbates and uses you for sexual pleasure. I feel betrayed?

So I've liked this guy since 10th grade and he's mean to me and tells everyone he doesn't like me. But then he goes and stares at me. My friend told me he told her he thought I was pretty. Then this year 11th grade, he almost tripped up the stairs trying to stare at me. My friend that knows him told me if he liked me he would flirt with me and talk to me. Because he did that with other girls he liked. But one day we were in class and he was staring at me and then he was going out the door to go to the bathroom and he looked at me as he was going out and he gave me a creepy smile then he was gone for like a long time and then he came back and the first thing he looked at was me. Then he got up from his desk and I was standing near him so he stood up and gave me a creepy smile and he had a bulge in his pants. But I don't get why he does this because he doesn't like me. He's told me and everyone else. He lies to me about everything and I feel so betrayed. What does this mean? Thank you. Xx (: