How do I forget about a girl?

We've been acquaintances for a long period... usually hang out in the same group of friends and we've been knowing each others for years. Only lately, I realized how much i like her as a person. I was really afraid about confessing my feelings to her and, in fact, she found another guy and they're actually dating.

I'm almost 21 yo and I've never had a relationship, so it hurts when someone close to me tells me about what it feels like to be in a relationship. i just want to forget about her, but i noticed i always associate people to places and songs, so every time I go out and see the places we usually go to, it feels terrible. I want to forget about her but it's so difficult.

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This attachment also influences my view of other girls... of course i see more beutiful girls every day, but she's simply unique and i can't find anyone like her
How do I forget about a girl?
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