Why does he avoid eye contact when I look at him but full on stare at me when I pretend not to notice him?

Basically the question. There's this guy I used to make eye contact with on a regular basis but now, whenever I directly look at him, he always avoids eye contact. Sometimes I see him out of the corner of my eye and he does make eye contact with me but looks away in a split second when he sees I'm not looking directly back at him. However, when I'm talking to my friends or doing something else, he keeps looking in my direction and at me (sometimes he turns his head to follows me around the room). There was one time we did actually make long eye contact (he was the one staring at me first and I just happened to catch him) and he didn't look away until I did a couple of seconds later. On top of that, he also tries to get closer to me (walk over to where I'm sitting/standing so that he's next to me, this has happened quite a few times) or even sit really close to me that our knees are touching for no particular reason.

Why does he avoid eye contact when I look at him but full on stare at me when I pretend not to notice him?
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