What would make a bully obsessed with me?

so this gay guy used to bully me and pretty much turned everyone against me. I never paid attention to him and did my own thing but he was obsessed with everything i did and hated when i got along with others. I made several friends and got along with others and he would hate it. I tried to distant myself from him several times but he still did something to cause drama between us. Now he is suddenly being nice to me but still obsessed with what I do. I STILL do my own thing, talk to my own friends, and he is still fixated on me. its been three years.

What would make a bully obsessed with me?
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