Why do I feel so guilty?

so this girl I was sorta "best friends" with, but not anymore, we pass by each other pretending like we don't see each other, we don't talk. Anyways this guy she was talking to, they were never official and he didn't want to be official. the first time me and him met was on the girls birthday party and he literally sat by me the whole night talking in a different language (were from the same country and everything) he kept telling me how he didn't like her that much anymore and he wants a girl form his country and the description he told me about the girl he wanted was literally of me. He requested me on insta later.
A few weeks go by and they stopped talking but this girl would ft crying because she really liked him and she wanted it to work out but he wanted nothing to do with her anymore. He lost interest and none of her relationships have ever lasted, so there's obviously something she's doing wrong.
He hit me up like two weeks ago and he was telling me that ever since that night we met he couldn't get me off his mind and he didn't want it to seem like he was going after her best friend to get back at her or something but we talked. Which led us to go on a few dates and we still talk and i actually see a future with him and i know he very much likes me. We go to different schools but we text morning until night and when we kissed for the first time it was so hot and it never felt like that before
Me and this girl stopped talking like more than a month ago and i feel really guilty. Why?
Why do I feel so guilty?
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