What makes a girl lose interest in a guy she likes?

Something like this seems to be happening to me right now so a little backstory here first

For about a year before she started talking to me she would stare at me a lot as would her friend and sometimes they would talk about me. I had a crush on one of her other friends and I talked to her but sort of failed, never talked to her again. She randomly started to ignore me after talking to her for two weeks and her bestfriend looked pissed at me. I tried to texting her if we could talk so I could ask if she was ok but she kept making excuses not to meet me and eventually ignored my message. Was finally able to talk to her in person but she wouldn't tell me what was wrong she just told me she was busy
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can't seem to be able to talk to her but it looks kinda like her friend is calming down I guess?
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I don't know now we just exchanging hellos and shit
What makes a girl lose interest in a guy she likes?
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