Spouse 44F cheated, how do i 39M let go

I '39M' am married to '44F' for 13 yrs now, together for 18. I have found many lies of hers over the years, including workers close to us that she slept with and denied, if she had cheated, ​body count, etc. Might not have cared if she admitted it when addressed but the lies went for years. She also had terrible post part and for 7 years I didnt see my family or friends, didnt celebrate birthdays, ​father's day etc, I just wasn't important. I was the bread winner and also gave her whatever she wanted- purses, surgeries, trips, you name it bc I had a sense that it was right, you dont leave bc it gets hard. One day she says shes snapped out of it and was 'back' and wanted to be joyful again. I was elated, but she then was getting drunk and being a bit flirty when we went out, with old flames. Annoying but not over the line. She then got hammered and gave my assistant a lap dance without panties at a major work event, and soon there after hooked up with a guy at a wedding I was also at. Eventually she admitted something happened but won't take responsibility. No proof but have heard this happened multiple times with multiple guys I feel as if I've been true to a person that wasn't to me while married, and sold me snake oil to get me anyway. She is now a great wife and is wonderful to me, but now I dont treat her as she should be. She deserves love, and I dont know if I can give her all of me, there is too much spite and lack of trust. Idk what to do. I could also cheat and then 'be even' and could move on, but that goes against my personal code. She is an amazing mom and i care fior her but cant seem to respect her anymre. TLDR; my wife was shitty for a long time and then cheated, is now amazing. How do I forgive and is an eye for an eye ok?