I'm sorry for cheating
Why did you cheat?
I thought I was in love with the other person, but that turned out not to be the case.
It doesn't make sense to cheat. It is good to apologize but it doesn't change the fact that you cheated.
I think that I'm the victim here.
I can't see how you're the victim. Cheating is wrong. You should try to make it up to your partner and be sure not to do something like that again.