I don't like him but I get jealous when I see him with other girls. Why?

this guy is my friend, and I like him as a friend. But whenever I see him with other girls I get really jealous. I don't even know why. I know he has a crush on me. So is it possible that I may be falling for him? Or I just like the attention?
I don't like him but I get jealous when I see him with other girls. Why?
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