Shes not a virgin and it bothers me so much?

Me and my girlfriend are both 16. She recently told me that shes not a virgin. She did it with a guy last year that she "loved" and they were dating. I felt really bad, shocked, and mad when she told me. Im a virgin myself. At times i tell myself like "shes used, why do i even want to be with her?" I get so mad when im by myself that i start to tear up. Idk why im like this. We have talked about it and her parents became strict because of that guy she lost it too. She told me she regrets it so much and every time we talk about it she cries. One time

I was alone in my room, and i just kept thinking about it. It got to me so hard that when i told her that i feel that we should end it she quickly called me crying and telling me that she was sorry. That she regrets it so much and that if she can go back and fix it she would. I just dont know why im like this. She told me that she's never been so in love like how she is with me and that she dont wanna lose me. I dont either, i love her so much, but for some reason i cant put her past behind me. :( please help idk what to do?