Guy's Behavior

There is this guy that is constantly staring at me....

There is this guy who was in my class last semester. He would stare at me all the time. At first, I didn't really notice him, but then I started to because he was staring at me. It was flattering at first. I started liking him, but got really nervous when trying to stare back at him, and trying to smile at him, so I just never did. There was this one time when I gathered up some confidence and stared at him; we were both leaving class and I just stood up and stared at him. He stared back at me; I was the one that broke off the eye contact. I thought that was really weird. Then I found out he had a girlfriend.. yeah, bummer. I had found out from a friend that has him on facebook. He's really confusing though, because why would he stare at me when he has a girlfriend? There was even a time when he was outside the classroon with his gf, and just when I walked past him, he hugs her... I guess trying to tell me that he has a girlfriend or something... So, I stopped trying to stare at him and started to not look at him anymore and ignore his stares. But I do still felt him staring at me. Then christmas holiday came, so I took the whole vacation to get over him. Since I am in college, we have a new scheduele so I don't have any classes with him this semester. However, when I saw him in the halls, he was staring at me. I am so annoyed. He is still staring at me! I sometimes get the feeling he thinks I am the one doing it to him and he's always trying to reassure me he has a girlfriend (by hugging her when I am there, etc.) but then again, I'm not sure. Then why would he be staring at me still? It's getting a little out of hand; kind of annoying and freaky. It's not flattering anymore. I'm not sure what to do. Should I go up to him and ask him why he's staring at me all the time? Or should I just ignore it? It's been almost 4 months now, and he's still staring at me. I try to pretend I don't notice it, but I really do. Any help, suggestions, moral support, etc. would be greatly appreciated!

Sorry it's so long. I am trying to condense 4 months of info. in my message... and there's still more!
There is this guy that is constantly staring at me....
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