I really can't trust my girlfriend anymore advice? (Long, long story sorry, serious answers only)?

Me and my girlfriend went out for about 7 months 2 years ago as a casual relationship, but i fell in love with someone else and ended it (admittedly a little bluntly), so she started seeing someone else and i tried it with the girl i fell in love with. After five days me and the girl broke up, and my feelings dissipated and i realised i loved the girl i let go, after telling her how i felt she admitted she still had feelings too, and not long after we kissed, and after about 4 months of us exchanging words about going out and whatever, we started going out. Now, we have been together for about 4 months, i knew she had s*x when she had been going out with the other boy but after i confessed that i didnt think i could sleep with her (as i have strong feelings about that sort of thing), she told me that she had lied to get back at me, and she hadnt really had , so a few weeks later i asked how far had she gone (in her life that is) and she said top off and that was it, i investigated, as i am a naturally suspicious person, and found that , that was a lie too, she had gone further up to , she then told me a long story (which i wont bore you with) about the fact she had only gone to , i at this point felt i could not trust her, and she finally admitted she did have s*x and that she was sorry, but after creating my account on here recently i viewed the questions she asked and i found alot of things i didnt want to see, and that even though i had shown her how much of my life i was willing to dedicate to her, including taking the slander off most of my friends and losing them respectively for going back out with her, shestill though i was cheating on her, and in her spare time her and a friend had taken to abusing me by posting questions. Now i feel i cant trust her, at all , and as much as i love her i feel that our relationship is heading to a break up and i cant stop it, im open to any advice anyone can give. Thanks.