Relationships and cheating

I need some advice. Me and my boyfriend have been together for 6 months now and are happier than ever. Although on Sunday night I found out that he cheated on me while he was out drinking on Saturday night. I was told by the female he cheated on me with. He was really drunk and told me he didn't know what he was doing. I confronted him and he admitted to it. He didn't deny what he had done. We have spoken about it and decided to work through it all. But it's all I can think about. How they done it,where they done it, how he kissed her or touched her. I can't get it off my mind. What should I do. I know that unless your out in the situation you don't really know but is it worth working through it. I'm at a complete loss.