Trust and Betrayal.. please help?

He broke up with me to go back out with his ex girl friend. We are best friends now, but it took a while to get over that. Alot went on with him and her that was bad and it kept getting worst, but we're always there for each other and always will be. It helped a little bit that we were pretty close to begin with. Forgiving him one was of the best things I have ever done in my life and it was totally worth it.