What does it mean when a guy looks a girl everytime he sees her?

I think it's been months (not sure since I didn't realize at first because I thought about another guy) that this guy looks/glances/stares at me everytime he sees me. Today, I was going down the stairs and he was about to go up walking behind his friends who are tall, I looked at him, looked away, when he was about to pass me, I looked up and he was already looking so we made eye contact and he moved a little to let me space to walk.

Later, I was queuing to enter the cafeteria and when he arrived he looked at me, then kept fixing his hair, looked again later (I looked at him also, that's not only him) sometimes from the corner of his eye. At the cafeteria, I was already seated with my friends and happened to look over my shoulder when him and his friends arrived, searching for places, they were looking far, at the back where there was a lot of places while he looked at me, they seated at the table behind (he sat right behind me). He pulled his chair quite far (a lot more than necessary) so it was close to me, I could smell a perfume, sat and during lunch, stretched his arms up behind (close to me again) many times. I don't know that guy.
What does it mean when a guy looks a girl everytime he sees her?
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