I need adive female preffered.?

i dated my ex for 3yr 10mo and then i broke up with her to see if i really wanted to be in a relationship. (we were talkin bout movin in possibly getting married). So during the break i hung out with a girl named mel that was total ***** and a gold digger. My ex thinks we had a thing but really we didn't. We actually ended up hating eachother. And for some weird reason she thinks that on our break i was out hooking up with all these other girls which is false. I was only hooking up with my ex when we were on a break. Prob not a good idea, but whats done is done. How do i get her to trust me again. I cheated when we were first going out, but i was 17 so it was diff. Every since then we had good communication and we trusted eachother. Advice please.......