Confused about feelings

When I met my gf we lived 200 mls apart.we built up our relationship slowly by mail and only saw each other a couple of times in the first 4 months. We slept together on our second meeting. After The first 4 months we saw eachother for a couple of days every week. 7 monthes after we met we had the conversation about previous lovers and she told me she had only slept with one person before and that was a bf of 6 months who she slept with 6 weeks before we met and that they broke up just before she met me. I was a virgin when we met. I felt very upset by this as I felt we had something really special but now it was spoilt. Anyway, deep down I Knew I was being stupid and it didn't matter and it wasn't really anything to do with me as it happened before we met. Slowly I got over those feelings(and I found it hard). Fast forward 3 years. New house ,new baby. Out one night I jokingly ask if shes ever been unfaithful to me and she says just the once. I was in total shock I didn't know what to do.She wouldn't elaborate on it and I didn't push it, how the hell could I with a 6 wk old baby (can I add here that my wife is a very reserved,shy,'honest',person). I had never had any reason to doubt her in the past as we always went out to places together and rarely spent time apart. It was never mentioned again and we moved on together and for the sake of my little girl I never said anything. Now fast forward 12 yrs and an innocent comment made regarding someone who asked her out at work a year after we married (she said no to the guy and I do believe her(she did tell me at the time it happened)) sparked the whole thing off again for me and I have had months of conflicting feelings. I have scoured our old letters and my memories and have managed to trace the time when I think the event occurred. It was 4 monthes after we met when we weren't really that serious. The guy was her ex. Now I feel like going and having an affair just to get even. The thought of this washes away all the negitive feelings I have but I know it's not right. Should I just forget the whole thing or am I going to feel like this forever......

Judging by the date on your post, I may be a little late. I just wanted to say that cheating to get revenge is wrong and it won't aid in how you feel. I was cheated on about 3 years ago and I had the same thought. After I thought about it I realized that it really didn't make any sense. My biggest focus needed to be on forgiving him and eventually I was able to pull myself out of the slump and actually talk to him about what he did. Your wife should tell you what happened, you deserve to know why. These are your feelings and she should have told you a long time ago. Talking about it with her will help you through, good luck