What do I do?

I live with my boyfriend and we've been together just short of a year and a half. Right at the beginning of our relationship, I made the stupid mistake of cheating on him by sleeping with someone else. He chose to forgive me and has generously forgotten it. However, he has recently cheated on me, by performing oral sex on his ex girlfriend. 
I guess we're even now, cause I did it first, but that was at the start of our relationship, and I thought we were happy together. His ex is pregnant with another mans child and she was the one who told me what happened. 
Do I forgive and forget, or move out and move on? 
Please only helpful advice, I'm hurting pretty bad and have no time for b/s.