Should I let the past go, move on and trust her? Am I wrong for fighting with her about this?

well, im junior in high school. I need help because for the past 4 years i keep getting answers i don't agree with or i just don't wanna hear and maybe they,re the truth. I've been with this girl for about 4 years now and our relationship couldn't be any better other than the fact that i have trust issues. Back in 8th grade we started to date and at that time we both were Little shy and weren't serious, obviously we're only in middle school. but about a month or so after we started dating we went to the movies,, her ex was there and i didn't know, but as i was sitting with her and she was holding my hand her ex was on the other side holding her hand, i thought he was some random kid but guess not. Then throughout the movie she went to the "bathroom" and friends told me she was kissing this guy. so once i found out after i broke up with her. i don't remember how but some odd reason i got back with her and throughout 8th grade we went on and off, we broke up a lot because of this guy. then one day he ****** her over by doing **** with other ppl so then she came back to me and from the end of 8th grade and on we we're together and she hasn't messed with him since, there were couple of times where he calls her or tries to communicate with her and she blows him off. we got more serious once high school started and we told each other everything and we're totally comfortable with each other. But christmas came and i was sent to texas to live with my grandparent for a bit, i would be coming back for sopre year. so this would be about 8 months. this was a big obstacle for us, but we wanted to stick it out so for about 4 months we did until we both decided it was to hard, then i spent the rest of the time single and both of us new i was coming back but never thought we'd get back together so we dated other ppl i dated 1 girl and messed with a couple of others but not while being with this other girl, I don't cheat anyways, she only dated one and of course he cheated on her. they broke up and then school came around and so did I. I saw her and we both were excited to see each other but had no intentions to get back..we were friend and from there followed benifits until we did it again and got back together. From then on things just skyrocketed, we lost our virginity's to each other which is a big deal for her because she wanted to save it for marriage but said she wanted her first time to be with me. She met my mother, my mom says shes one of a kind and that every time shes with me she seems so into me. shes met almost all the important ppl in the world to me and all of them thinks shes great. her mother which is really strict, even became fond of me her dad still hates our relationship, now we do everything together and love each other soo much. We fight a lot mostly because of me and my insecurities. she doesn't really even fight back because she feels like she deserves it even though she has repeatedly said sorry and told me shes ready to only be with me. I don't she deserves it after this long. and lately im seen as a because im jealous all the time and untrusting but she doesn't give me any reason to suspect shes cheating. The old ex calls her now and then but she doesn't want anything to do with him.