OP, I'm 10 years on from finding out. I never, ever thought he would betray me like that. I adored him - down to his bones, we'd been together since I was 19, I was as loyal as anyone could be to their partner. But for pretty simple reasons he ended up cheating for a couple of years - maybe more. I will never know the full truth of it. None of us will ever know the full truth of what went on.
It was horrific, the aftermath years. He did everything he could to "make it up" to me; bought self help books to "find out why" he cheated (it was pretty obvious the ego boost and sex were an addiction for him, but whatever), gave me all passwords, bla h blah blah. I had horrifc nightmares about it for the next 7 or 8 YEARS - I would wake up shaking and crying. It 's faded recently, but a decade down the line, you never quite ever trust them the same. Everything changes. You change. They are not who you though they were - they are now proven dishonest, disgusting, vile liars. They lie, easily - and well. So, you will never know, for the rest of your lives together, what is real and what isn't.
I agree with pp - I became the kind of woman who just looked at him and thought, "do what you fucking want. Because, you;ve scarred me so deeply, I now feel numb about you. Do what you want - I just don;t care the same anymore". The betrayal is so awful, so horrific, so utterly lifechanging, that the scars that form can never be healed.
Do I wish I'd left? I honestly couldn;t leave him at the time,for financial/work reasons. In one way, I'm glad I stayed, because it got me my beloved children. They are my world. They are all I care about. But it's obviously different for you as yours are grown. Had "d"h done it to me after the kids had grown...yes. I would've left. And never looked back. I also would've never trusted any man ever again - I;ve seen it happen too many times, to too many of my female friends and relatives. It may be an "irrational" feeling, but I would never, ever enter a relationship with one again because I honestly feel they have their normal, every day persona, and then there's the dark hidden side, the ego, lust side of a man that is just an absolute Hyde to the Jekl of the side they show friends/family etc.