Why did she turn her back on me like that?

Anonymous
This girl showed signs of interest. I started to fall for her. I also started to show interest. Some other girl noticed and befriended my crush. Not sure if that other girl confessed to my crush forcing her to back off, but she had this behaviour of hot and cold/ignoring. I got tired and asked her what is happening. She said it's nothing of that sort. I was ok with this. she started to ignore me. I got confused so i started to ignore her back. I made an effort and somehow started to talk to her again. I confessed and asked her... AGAIN. She said no, she goes and sleep with some other dude. I stop hanging with the group. Fast forward 1/2 year, we bump into eachother on the street. i say hi, she answers and stops to ask how am i doing. I tell her i am good and keep walking.
Fast forward another year, she was waiting for someone. i was heading in her direction, we see eachother and... she instantly turns around... facing a wall. i passed by of course.
Why did she do that? Help me understand this.
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don't tell me this questions is too long and there's too much to read
Why did she turn her back on me like that?
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