28M and 25F, am I leading her on?

We have been together for 9 years. I broke up with her after 7 years because of alot of arguing and stress of lots of little things and during our break up, I was hanging with this girl, only to smoke, and she ended up trying to kiss me. I stopped what she wanted to do because I wasn't attracted to her. So fast forward 7 months of no contact, me and my ex run into each other. (Also while we were apart, she slept with another guy In a one night stand) I ask to get back together which she agreed. I never told her what happened(which I know was wrong) and she ended up going through my phone and found msgs between us about smoking. My girl called her and she made up a whole story about what actually happened. I did lie to her about the kiss at first cause I didn't know how to tell her because of the way she overreact. I did end up telling her about it but she didn't trust me or believe me one bit, so that summer it started the worst and we fought almost everyday for hours for 2 YEARS straight. I finally broke and told her I wanted to cancel our wedding and end our relationship because she didn't trust me. She then tells me she'll trust and beelive me because she doesn't want to lose me. I just don't understand why it took this extent? I feel I don't trust she won't turn back once we are married. She does alot for me which is why I'm having a hard time but I've tried to be the best, most loyal man I can be but I just see myself with someone else now. I don't know if I'm just hitting a low or if I should follow my gut and just end it before I regret it. I will never cheat especially after what happened but I don't wanna keep leading her on if I'm just forcing my feelings. Some advice would help. I'm just feeling really stuck with this. Also this is my one and only relationship I've ever been in, as it is for her