I can't trust my girl and I love her but I just can't trust her. What should I do?

I love my girlfriend but I just can't seem to give her the trust she want. Let me first start off by saying my girlfriend to me is way out of my league. The girl's in my dreams ain't as beautiful as she is and I love that she loves me and lets me make love to her and things. We've been together for nearly two years now. She has cheated on me twice. The first time was two years ago when we first got together she was a major player and she played guy's all the time and she played me but then she fell in love and I changed her. Then the second time was last august she got another boyfriend while she was with me and I didn't know because we go to different schools. Her cousin hates me and her dad is really mean to my girlfriend and doesn't allow her to have a boyfriend but her mom side of the family does like me. But her cousin told her if she finds out we're dating then she'll tell on her so she got another boyfriend as a cover-up. They never kissed or went out or anything. They just hugged and this dude was not my girl's type at all so I took her back and she dumped him. But those we're the only two times I know that she cheated but she's very beautiful and lots of guys like her so they be trying flirt with her and be smacking her *** and running. But she doesn't get along with other girl's so she only hangs out with guy's but most of those guy's like her and it's real hard for me to trust her because I know how guy's are. They want to get her trust as a friend and when she's weak they will strike. I want to trust her but I can't. She says I'm insecure and that she loves and only wants me but it's hard for me to trust a girl with 1000 admirers. What should I do?