My girlfriend cheated on me but she denies the whole truth. What should I do?

Anonymous
Me and my girlfriend have been dating for 2 years now. She has cheated on me during the second week I was with her because I went out with my friends biking instead of going out with her. It sounds so stupid doesn't but the worst part is that lately I found out that she had more than just kissing with the guy ( she told me she just kissed, no sexual intercourse). I messaged the dude and I ask him about that night and he told me he had sex with her. When my girlfriend knew about me talking to him, she started panicking. She started telling me what did he tell you and stuff. When I finally asked her the question about that night she denied everything and said she didn't have sex. She even swore to me on her grandpa who is very important to her, even more than her parents.I trusted her and believed her. In another occasion, I asked her again because something was telling she wasn't telling me the truth. So when I did, she hang up on me on Skype and started messaging on what's app telling me stop messaging, get away from me and sh**. She even told me, I'm gonna block you if you don't stop asking me this question. For 2 years she lied to me and never wanted to admit her mistake. She told me wait till we all meet together and if you have proof that I had sex I'll leave you alone and never talk to you again. I proposed to her to tell me the truth before I know it from someone else and everything will be fine but all she did was yell at me and tell me that my life with you is hell even though everything was going great. What should I Do ? I really love this girl, but I can't live with the fact that someone had sex with her while she was with me. Please help me.
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+1 y
she admitted to me that she did more than just kissing and we got in a fight. she spit on me, hit me, insulted me while I was the one hurt. I couldn't control myself, I slapped which I felt really bad about. She started crying I tried to hug her, I started to cry like crazy but all she told me is I don give a fuck about how you feel. I have no one in the US, the reason I came to the US is for her.. The point is I wanted to make her my wife but I can't deal with knowing this fact.
My girlfriend cheated on me but she denies the whole truth. What should I do?
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