I'm going to break a promise to my already broken boyfriend
Did you break your boyfriend?
No, I found out and he should have told me earlier.
It is wrong to be dishonest in your close relationships. If you break a person's trust you might not be able to get it back.
It's fine; it's not like I'm going to take him back. I'm going to cheat on him first.
Cheating is never the answer to a bad relationship. You can always break up first before doing that.