Guy's Behavior

Why is he pretending not to notice me? :(

We have both crushed on each other for like 7 months in college. He always spoke to his friends about me. He always followed me around college. He flirted with me in lesson but he used girls to make me jealous in lesson. I always heard him say to his friends that I'm good looking and that he likes me. 7 months later, I saw him up town. He said to me that he likes me but has a girlfriend. He said he couldn't help looking at me. Anyway, he's single now. He saw me out on a Saturday night followed me around the night club and stopped on a step. I wasn't sure if he was in a relationship or not so I just walked past him. A week after he started kissing girls in front of me to make me jealous and he ran off the dance floor when I danced with someone and left the girl he was with. He kept staring at me. But for some reason now he is not looking at me. I don't get him, he tells me he likes me but is in a relationship, but now its like he pretends not to notice me. Is he playing mind games with me or is he just suddenly not interested? Also, what should I do? Should I just walk up to him and chat him up? he's really good looking so girls always come up to him. I want him to chase me but I don't think he will do because he's acting like he doesn't see me. All his friends keep looking at me. So maybe they know? but I have no idea why he's acting like this. We're both 18 years old btw.
Why is he pretending not to notice me? :(
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