Why can't I stop thinking about this girl, and how can I move on?

I've been stuck on this one korean girl who I've liked for a while. I've never had the chance to confess to her because I wanted us to have more time to connect and also figure out if she liked me in the first place or had any interest with me. We both were friends and talked and played quite a lot in and outside school. Though I didn't see her in the next school year because she moved so I couldn't really interact with her but in-between that time, I for some reason (don't ask why, I've been questioning myself about it for like 2 years now about it and regret it...) decided to I think out of jealousy or something else I really don't know unfriend her and block her. I feel like the stupidest man alive and I swear if I didn't make that one stupid decision in my life we could've been much more. I wrote her a long apology on Gmail because that was the only remaining method I could use to talk to her in August and she accepted it though seemed pretty confused. At some point we stopped talking and like months later after we haven't talked in so long I just decided to forget it and unfriend her to try to move on since our friendship was practically broken after I ceased contact with her and she went to another school. About a year later I fell in love with another girl who I also didn't end up getting with and after I got over her the korean girl I began thinking about again after when I was trying to figure out signs about a girl liking you. She probably didn't like me but I noticed that she was glance at me when we were sitting at different seats in class a few times, asked one time why I leaned closer to her after I couldn't hear her in a loud environment, she replicated things that I did many times, she acted slightly different when around me, and a few other things I think. I really REALLY regret doing this and hopefully she attends the same highschool that I'm attending because I really want to try to make up for what I did and hopefully we can become friends again.

Updates
8 mo
I've been frequently thinking about her and have been constantly reminded of her due to things related to her and I've been constantly thinking of her. I don't feel like telling one of my close friends who still in my classes about this because they were also pretty close to this girl that I like, and also they would ship both of us together so telling her this two years later even though she already known's that I have feelings for her still makes me look pathetic and weak.
Updates
8 mo
Also mb for posting this in the wrong place, don't really go on this site.

Why can't I stop thinking about this girl, and how can I move on?
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