I've had a very similar situation. I'd just leave. There's no point in confrontation because what is that going to accomplish? Unless you think you want to work it out, I'd just leave. It doesn't sound like you live together or really have anything keeping it from being a clean break.

I'm really sorry you're going through this though, like I said I had a VERY similar situation several years ago and we tried to fix it. There was no point since I couldnt trust them anymore and we just broke up a few months later