Why are boys obsessed with staring even having a girlfriend?

So I have this classmate who used to stare at me a lot. He once talked to me also out of nowhere. Always sat beside me. I could feel him listening to me whenever I was close to him and talking to someone else so I thought he had crush on me and will approach me. But it turned out he developed situationship with another class girl who was after him and still stared but less frequently. He avoids her in person but is involved with her online. Once my friend told me that he was talking about that girl that she's too obsessed with him and he doesn't like her but then I saw him with her so many times. Why doesn't he stop looking at me if he's interested in her? I mean why men do that?

Why are boys obsessed with staring even having a girlfriend?
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