Sorry to hear that. It's his fault for not being faithful to his GF. If he didnt want to be with her, he should have had the respect to end it with her and let her move on with her life.

But it's time for you to move on as well. If he's anothers, then it's over. Its hard to hear, but that's it. You just have to end that chapter in your life and move on.

Things happen, we're all human beings.