Why is my ex-boyfriend suddenly avoiding me?

My exbf broke up with me 6 months ago and we were together for 10-11 1/2 months. He broke up with me because he lost interest and I changed my persona. Since then, I’ve worked on myself and my self-esteem greatly, so, we talked regularly at a party, at school (we share the same social circle) and we laughed, had a great time. He seemed fine with me, but then something changed during the months of October-November, there was a party which he and I attented along some of our friends, and that day, he started avoiding me, if I was in front of him, he’ll automatically leave and so on... This has been going on since this day, I haven’t talked bad about him, I haven’t done anything mischievous to him, nothing. So I scratched out the reason that he may be mad at me. I asked one of my best friends, which is HIS best friend, too, about why he’s doing what he’s doing, and my ex said that there’s no reason why he should talk to me, we have no business together, nothing. But he said different things to other people, I don’t know which one is true. I do not want to reach out to him because I did once and he almost didn’t respond. Since we don’t “have any business” together, he still stares at me (A LOT) in school or whenever we’re in a party, he just does it and sometimes doesn’t look away. As far as I’m concerned, he doesn’t want a relationship after ours and only wants to “hook up”. He’s not seeing anyone, as far as I know. He has tried to make me jealous, I think, but I’m not sure at the same time. What is this? What is he trying to do? Why is he doing it?
Why is my ex-boyfriend suddenly avoiding me?
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