If not, I'd suggest never letting him find out you bedded her before the breakup.

VERY good advice!

I think it's possible to find a diamond hidden in the rough there, you just have to be patient and take a look at everything from as many angles as you can, and just be careful. A lot of emotions are on the line right now, on all parties. Take your time with things to make sure that these feelings are real, and that the emotions aren't making the decisions. Decisions based on emotions can tend to be clouded, and one sided. Thus, leading one to make a hasty and bad decision. I know this first hand. I almost lost the love of my life because of it. Luckily she didn't want to give up that easy, and I had some friends that helped me step back and take a look at what was really going on. Now, our love is stronger than ever, but had I stuck with that decision that was based on emotions, I would have lost the best thing that's ever happened to me!