You're in a terrible spot, and I empathize with you.
In my last relationship, we were together for two and a half years. One year in, I found out he cheated. I walked in on it (literally, as they were fucking), and I will never forget how intensely I cried. "Baby, I never want to see you in so much pain ever again. I am so sorry." yadda yadda yadda... for the next year and a half of the relationship, I kept waiting for the other shoe to drop. There's no other way for me to describe the feeling that one day, some how, something "else" would happen.... not even sure what.
A year and a half after that, after so many "late night check-ins," after so many "I love yous" this happened:
It was a Saturday morning, in January. He had to go to work that day, and was going to be at work from 1pm-10pm, but he me up around 8:00 as he was getting dressed and said "Baby, I'm sorry, I gotta go, there's a problem at work and I have to head in there now." I was disappointed because we were going to grab brunch together with my friend for his birthday since he had to work that night and would miss a little dinner get together. The day goes on, and we after dinner we were heading out to a bar for a drink and I sent my boyfriend a text telling him we were heading out for a drink and to stop by after his long day at work. But, he never got my text. I ran into him at the bar, on the dance floor, making out with somebody else; a coworker he worked with, and I had met about a month prior.... they went out to dinner after they got out of work, at 6:00 that evening.
Being cheated on hurts not because of the actual act of cheating.... I consider it to be throwing down the wild card in a mental game.... it changes the rules and the expectations for the rest of the relationship.
You have to make the right decision for yourself, but the first question should be "Do I deserve to feel insecure, until I am able to feel secure again?" I wish I listened to my gut.