Why does my crush keep an eye on me whenever I talk to other guys?

He always keeps an eye on me whenever I talk to other guys and has this worried or annoyed look on his face. I have a lot of guy friends and all I do is talk to them.

He also keeps staring at me whenever I'm not looking and quickly looks away if I catch him.
Why does my crush keep an eye on me whenever I talk to other guys?
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