What should I do about us?

Ok I have been dating this girl for over a year now and I still lover to this day. About 3 weeks into the relationship I had sex with another girl when i was shitfaced drunk and that doesn't make it ok or anything just details. ok 3 months into the relationship my girlfriend when to her friends house and drank 1 and a half of four locos and both kisses and sucked on each others necks and ****. I told her what I had done about 2 months into the relationship because it was bothering me and i had to tell her she stayed with me even after what i had done well she didn't tell be about what she had done until 8 months after about 11 months into the relationship only after I told her it would be ok to tell me I wouldn't leave her or anything in those 8 months i told her that i thought she was or had cheated on me several times and every time she told me I wouldn't do that to you im not like your other girlfriends. Swore on her own life, my life, and her family's that she hadn't or wouldn't do that to me and they were all lies she made promises that she hadn't and wouldn't and i believed her so my problem is, is that I don't trust a thing she does to this day and have a hard time believing her with anything and its driving me insane making me angry at her all the time and just putting me down and down so I would like to know what you all think about this whole thing and what you think i should do I lover her to death its just so hard to stay with her when i feel like this but i can't bring myself to leave her no matter how hard try ii can't i love her to much