Why won't this guy follow me back on Instagram?

There's this guy I like and one of his friends said he like me back. I followed him on Instagram two months ago and he never followed me back. He's following other girls and stuff but he's ignoring me. In the end, I just decided to unfollow him because I felt so stupid. Do any of you guys know why this could be?
Why won't this guy follow me back on Instagram?
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