I found this script thread helpful too:
www.mumsnet.com/Talk/relationships/1527705-Midlife-crisis-this-is-the-script
It's not just men. I had the same with my wife, albeit she (alleged) it was never physical. I would put money on it being so now. We've separated for about 3 months.
If you're like me you'll be blaming yourself a lot in the immediate aftermath. Ironically my wife told me I was a fantastic father and that she admired me and we actually reached it's "not you but me" (see the script) but I've read it's natural for victims of trauma to blame themselves - it's the brain's way of assigning a bit of control over something that's completely blindsided you. It sounds messed up, but if it's all your fault then at least you could have stopped it or can stop it in the future. As it is, most likely there was nothing you could have done - you tried your utmost and it wasn't enough.
It's hard to accept that as its frightening. So ride the wave and get as much advice and comfort from friends and family as you can. Let them keep you on even keel. Don't pent it up. Eventually you'll get some clarity. You'll stop beating yourself up.
I'll also second cutting off contact as much as possible. For people like us, with kids, obviously this isn't completely doable, but I found keeping discussions to texts and emails and being as curt and business-like as possible helped. As soon as possible I ensured there were boundaries for kids visiting times so we all knew what was going on and I had to do as little day-to-day negotiating as possible.
My wife, naturally, wants to keep things as "normal" as possible - to stop for a cup of tea, even go on holiday together FFS (bet loverboy would love that!) but, as tempting as it is to do it for the kids, for the sake of my sanity I've resisted. Often it's only to assuage the cheater's guilt, keep up appearances and stop everything being so inconveniently awkward (for them - like "hey, everyone, we're all fine now and everything's just the same except we don't kiss anymore!") If nothing else, I'm not comfortable doing this as it suggests I condone what's transpired. I may eventually understand it. I may eventually forgive it. But I could never suggest what's occurred is anything other than an incredibly traumatic event - at least for myself, our kids and close friends and relatives.
Try and keep your dignity - you have the moral high ground and if you behave professionally it will be recognised. Don't stoop to petty insults and bitchy remarks if you can help it (you're only human, so if you're like me they will slip out! That's fine and its probably cathartic, so long as it doesn't become a habit. I just warned certain friends of the possibility of it happening and apologised in advance! They were very understanding). I've been astounded by the support I've had back, even when I never asked for it. I got used to acquaintances at the school gates looking at me with abject terror whenever I appeared, but quickly learned it came from a place of not knowing what to say - the sympathy is there, often, it's just people don't know how to deal with it. Now I understand, it's fine.