I go over this myself, not specifically because of infidelity, but over other issues with people. I'm not a forgiver. I'm a "oh, so that's what you're really like, now I know, and screw you" type. Not about everything or even most things - most things even if I get very angry initially, it blows over because people make mistakes and have legit accidents (cheating is not an accident, of course) but when I feel I have been personally badly treated or deceived or manipulated....THAT I don't really want to forgive. It's a warning, it's a "that's what YOU are REALLY like". When you find out it's a snake, remember it's a snake. For me, I think it's about my self respect. I had an extremely difficult childhood so the idea of having self respect and right treatment IS very important, to me, it's a survival issue. I WILL NOT put up with abuse and I'm willing to fight back, physically if I have to, to save and protect myself (and others). So....I don't know how that fits in with forgiveness, especially the Christian ideals we all grew up with and that just didn't take with me. To me, it seems like weakness and letting people get away with bad stuff. And I'm not one of those who thinks that not being forgiving hurts ME, I don't feel that way. It's about having boundaries, not putting up with mistreatment and not interacting with people that have abused me, and giving them even more chances to abuse me. Maybe you have to feel you have more at stake by NOT forgiving the offending behavior - cheating in this case - than just by moving on, which is what I would generally recommend. I don't think recon works in general, I think the basic betrayal of infidelity lives in a corner of people's hearts, probably forever. You don't forget what they are capable of once you've seen it....it's a part of their character. And most people DON'T change. They can, theoretically, but they don't. These traits are always waiting there, to me, just for the right opportunity to come out.
It's a slow poison and for me, it's better - for both parties - if one can cut it out and start fresh. End that relationship and either don't interact or as little as possible, or at least wait a period of time to try it again if there's some reason for that, and try to start fresh if you think there HAS been actual change. I tend to put the past in the past by putting the people in the past as well.
That said, there are always lines in the sand and our lines may be different. With my husband I have got past his cheating attempts which were online dating apps (he never actually met anyone and I do believe that - he just wanted to pretend to be someone else with a more fun life during a bad period of time), and a long term (decades) EA with an ex girlfriend, which has romantic overtones but I think it's just been a friendship for a long time. They are widely separated by distance and life experience and he's not an adventurous person anyway. Have I forgiven these? I don't know how to characterize it....for me, I just stop caring about some things after a while, because I always prefer what is new or what is in the future. So as long as I know it's over or not of any significance, I stop focusing on it emotionally. I can still get triggered at times, but it's less and less. It is not active forgiveness...it's more like "not caring". It did permanently change how I regard him. I don't have romantic or sexual feelings for him anymore and I don't think that will ever come back. Once that's killed I don't see how it does. But I am fond of him, I do love him as a friend, I try to help him, and we are good roommates. I think it's the best relationship I can achieve at this age and with my health condition, etc. I am sad that this marriage did not turn out as I would have wanted it to or what I think marriage should be, but I feel that way about life in general. I'm not pleased with how anything turned out and I blame the circumstances I was born into and unfortunate choices I made along the way that didn't improve things. So it's not really about forgiving but more about forgetting, and that this is just the most practical way I can live my life. Now if he suddenly decided he wanted a more romantic, traditional kind of relationship, I would have serious problems with that and I don't think I'd want to continue, but that would present real practical problems for me, especially in this economy.
I wouldn't worry about "forgiving " - I really do think it's a bunch of bullshit that's forced on us by others to make their lives and society "smoother" and easier. I'd focus more on....WHAT DO I NEED AND WANT? What do I need to be happy, successful, or even just to survive (many people DO live at this level more than we think). What is acceptable to me - there is a infidelity writer who is NEVER mentioned on this site, and I don't know why as I think she is the best, but I can see the taboo, who asks the basic question "Is this relationship acceptable to you?" and I think it's a great question because it gets down to the heart of things, your gut feelings about how you feel and what you want. If it's acceptable to you, that's your answer....if it's NOT, that's your answer too. If you're still being bothered by these things that happened so long ago maybe the answer is: This relationship, at its core, is NOT acceptable to you. For whatever reasons. Don't worry about forgiveness - worry about what you WANT AND NEED. Now if there are kids involved, responsibility to them becomes part of the equation too, but at some point it just becomes the two of us, and that's the main question to me: Is this relationship acceptable to you?