My Girlfriend Told Me She Likes Another Guy?!?!?!

For the past week, I had been noticing a change in my girlfriends behavior. She seems less interested in me, and talking to me. She has admitted to me that she is a very flirty person, and although I can't stand it, I often let the fact that she flirts with other guys go. The other day she told me that she liked another guy. She said that this did not change how she felt about me, it was just a crush and she would get over him soon. She blamed this on the fact that we don't see each other much (because her parents don't even allow her to date) She thought I was going to break up with her but I didnt. This made me unbelievably sad but I knew I couldn't break up with her for her or my sake. After it happened, I asked her best friend if anything else happened. I found out that this guy she likes is two years older than her. I also found out that she was going to go to his house and have sex with him. However, as much as I hint at it my girlfriend still won't admit this to me. I really don't want to break up with her, I just want to fix things, someone please give me some decent advice, I really am in need.
My Girlfriend Told Me She Likes Another Guy?!?!?!
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