I don't think the choice before you is as clear cut as saying there is one path that is difficult but right, and another which is easy but wrong. It's great that you are thinking about the consequences of your actions, but shielding the family of the guy your ex cheated with isn't necessarily the right thing to do. Simply holding back your anger is not necessarily the right thing to do. This is why I think talking this over with a counselor is probably a good idea.
How many guys end up cheating, really in the end. Even if we are just taking about a trip to a brothel in their lunch hour. Maybe im cynical and negative, but i think it ends up being almost all of them, close to 100% of them. Then there are all the cuckhold ones, then there all the ones that want some secret man action, which beyond 40....well you dont want to really know. And how many womwn believe their men going to cheat in some way eventuallly anyway, regardless of affirmations to the contrary.. Im very sceptical
It's been a while since this happened and here are some updated thoughts... Anger subsides over time, and I'm no longer angry. A whole bunch of the trust issues haunt me whenever she's not right here with me, but they're not as sharp as they were. Soon after I posted the thread here, I made a decision to not do anything stupid and leave myself in a worse situation. As I calmed down, I let her believe this is something we could put behind us and let us move on to an even better place. I'm not at all sure that's going to happen but her believing it has led to a more peaceful household, which to me is very important. On her end, she's shown a deep regret for whatever went on that seems very sincere, and I promise I'm hyper sensitive right now with my BS meter. She's also been very upfront about the depth of their relationship. They've known each other since before high school and never dated or hooked up. They remained in contact through her twenty year marriage, and her relationship with me. Calling before texting was the norm, then texting. She's let me see all of their communication from before I even met her to the night I saw them in his car. Two phones worth. While some of it was a little more risque than I feel is appropriate, none of it actually shows that they ever did any more than talk whenever they met, which by timelines of communication was never more than 15 or 20 minutes. He always appeared to be more aggressive in trying to see her, and she liked seeing her friend. When I saw them together, all I saw was him leaning on to the passenger seat obviously kissing her. It's her story that this was the only time that ever happened, and he did it literally the second I was walking up. I'm not sure I can believe it, but reading all of the communication supports her story. He's, asked repeatedly over years how she would feel if he just grabbed her and kissed her when they met, and no response ever indicated she'd be ok with it, or that it happened and she enjoyed it. So here I am with woman who I cared deeply for who knows she did and was doing something she dam well knew I wouldn't be ok with, but the evidence doesn't show anything but a platonic, but maybe escalating relationship that she kept from me. Im also having my every desire catered to, exactly as it was plus some. With all this taken into consideration, I'm still in my home, with a calm atmosphere, and working towards a future where if I leave it'll be when it's best for me with zero thought given to how she feels about it. Of course there's the possibility I get sucked right back into our long term plans, but that will only happen if it truly doesn't matter to me. I won't spend a second of my life wondering if my partner is hiding anything from me. So that's where I am at this point, and I'm comfortable enough to let a little more time pass before I make a final judgement. A huge thanks to everyone who took part in this with me, it was an outlet that I needed way more than I realized at the time. Onward and upward with no regrets.