Yes, we all hear these apocryphal tales of couples 'getting through it'. Often on websites where they're selling something.
Getting through this, one way or another, is in fact your only option. Even if you split up with him, you're still going to have to get through it. In many ways, what you do if you're trying to stay or if you're going is just the same. If you leave, you may think you don't have to deal with it - but you do. Your only way supposedly not to deal with it is to demonise him - he was just a shit, he might have seemed good in some ways and you might have thought you loved him, but how could you love such a bastard? He's worthless.
And yet, under all that, your deep feelings are not that. Just because you found out he betrayed you doesn't make your love go away. Just because you know he behaved unkindly and badly doesn't erase that whole world of love and closeness that was yours (plural). It doesn't make that go away. That's still there. And what is so horrendous is the co-existence of the feelings of love and of his importance and of him being yours, and the knowledge that he has betrayed that. That he has touched another woman. That he has lain in her arms. That he has kissed her. Looked in her eyes with desire. That he has held her. That he has fucked her. And that it has been so exciting and intoxicating for him that he's done anything he could to protect that new paradise he and she created for themselves.
And, if it was such a delicious thing that he had to hide it and carry on for 10 months+, how can he leave it now? How can those tracks be erased? How can that world disappear?
Well, simple answer is that it can, and it might, but only under certain conditions.
It had to be mainly just lust. The chase. Mostly sexual infatuation. Not much of a fit in other ways and not much of a life-fit.
And she has to have let it go. Lost interest. Moved on. Decided, for whatever reason, that fun as it was, it's not for her.
And he has to feel like shit. Really bad. Inconsolably bad about how he could have lost his head like that. And really really desperate not to lose you over it.
And you have to have had a really good fit, in all ways. You have to have been genuinely good and compatible.
If those factors are ticked, then there is a small chance. But the last bit is down to you.
I don't know the details of what he did, but it's usually fairly standard. The issue is whether you manage to forgive him in the first instance, and forget in the long term. I'm not sure whether this is possible. You might just have to live with the wound, and for it to fade over time. You have to actively work on healing it, with him.
The last problem (and this is a big one) is:
Will he do it again?
Once he's learnt how to do it, will he be tempted again? Because this time it would be a hell of a lot easier for him.
As for your feelings now, yes, shock, losing days, reeling, panic, genuine madness - that's the first 10 days or so I think. Then disorientation, redefining yourself, redefining him, not wanting to. Details? I'm not sure. The instinct is to want to know everything, but of course any detail becomes etched in your brain and will torment you. I suspect that it is actually better not to know. As others have said, he will probably not tell the full truth anyhow. Probably good to know about a few really monstrous lies - eg, that you were working and being good and worrying about dinner and being nice to his mum/kids/grandma while he was supposedly honestly engaged in some commendable task somewhere, but was in fact reassuring you on the phone while fucking this woman in some car or hotel room or wherever. You need a few solid examples of that, so you get a sense of the extent of his lying and selfishness.
It's down to him, her, the detail and - ultimately - you. You have the last say here.
If you (plural) do get over it, you will not be the same again, anyhow - nothing will ever be the same. It's a different world now. Like after someone important has died. This is grief you are feeling, as much as anything. It will take about 2 years to start to feel you're pulling out of it. Possibly quicker if he behaves properly.
But 10 months is quite a long time. This isn't a drunken misdemeanour. This was a campaign. A habit. An intimacy.
Wanting to make him 'pay' isn't the answer. Wanting to understand why might help. If he will share with you, it could help.
Good luck and just remember - you've been in an emotional car crash. A horrible shock. Everything feels weird. But you will get over it. You will.