Why so weird this guy?

There is this guy who has been glaring at me a lot to the point where it has mentally affected me. We know each other from childhood. We dont talk to each other at all. Whenever I look at him he looks at me like I am some creep. I dont know what he talks about me behind my back. He watches my instagram story very quickly. With others he is very normal. Should I confront him? How should I? Avoidance is not the solution because it is mentally affecting me and when I see him he is always enjoying, chilling etc. He knows I had a crush on him.
Why so weird this guy?
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