Ellie, I really feel for you. Reading your post took me back to around this time last year when my whole world fell apart. I know exactly that sick feeling you are experiencing now, you can't eat, you don't sleep, the only thing that keeps you going is your DCs. My DH of 8 years had been acting "off" towards me, saying we didn't get on anymore (which was news to me!), that he kept wondering what it might like to be single again. All very odd and completely out of character. He also kept taking his phone everywhere, to the toilet, EVERYWHERE! I confronted him and he denied any affair, but speaking to friends they kept saying it sounds like an affair. I suppose deep down I knew it all along but didn't want to face it.
I have his email password (he is not very techie, so I set up his email account for him) and I have never checked it before. A did consider doing do when he began acting strangely but I remember worrying a out what I would find, until one day I couldn't take it any longer. I found emails to a work colleague, stuff like "morning gorgeous, you're looking looking so hot today". And it was at that moment my world fell apart.
I rang him at work, told him to come home and pack his bags immediately and that I would be filing for divorce. At that point I was on auto pilot. He didn't deny, but said it has never been physical and begged me not to kick him out. I stood my ground, then hung up and emailed this colleague saying I knew what had happened and that she was welcome to him, we were finished. She replied saying it was never physical, she wasn't interested and it was he who had done all the chasing (not sure if this was meant to make me feel better?!!).
Anyway, he came home, begged me not to divorce. I said we needed counselling which he agreed to. Went to a session that week but TBH it was all too raw and I was unable to take anything in. It was too soon (as I suspect it may be for you) but I would suggest you have counselling on your own to start off, to get your feelings out.
After a week I couldn't bear the sight of him, every time I looked at him I felt so betrayed. So I kicked him out for a short time and it was the best thing I ever did. DH is a teacher so I got him to stay with a friend for half term (1 week), I wish I had made it longer though.
Whilst he was away he rang every day to speak to DD (then 2.5) and I refused to get into any conversation with him. I also went out to see friends as often as possible in the evenings, if your family are local I'm sure they would babysit (esp as they are so angry with him, as mine were). I know it really got to him that when he rang in a Saturday night I was the one out enjoying myself while he was the one sitting at home watching X Factor. I should add here I am tee total so would always drive home and be able to cope with DD the next day!).
He came back a week later, didn't seem to be that different, I told him to go and stay at his Mum's with DD for a few days (MIL was on my side). She seemed to talk sense into him, he came back, we went to counseling every week for about 2 months but had to stop when it became too expensive (£80 p/w).
So that was all a year ago. Since then I have shown up at EVERY school function (school is a private school so there are plenty of functions) and always been outgoing, chatted to everyone so that OW knows I have every right to be there and SHE is the one who should feel uncomfortable in that situation, not me.
DH has returned to being the loving, devoted man I married. I do think there is something to be said for mid-life crises which is not an excuse, but I feel this was a MLC in part at least. The trouble is, what we had was broken and will never be the same. That is what you have to ask yourself if you can live with.
I still think about what he did to us on a daily basis, every time his phone beeps I am suspicious. He has offered to look for a new job, but the thing is, if it hadn't been this woman it would've been someone else. As someone else on here has said before, affairs are addiction and it is the attention, excitement and taboo that he craves. And that is what stops me moving on completely, I can never offer him all those things in the way someone new would.
DH is OTT caring, loving and considerate now, he absolutely dotes in our DD and anyone would think we are back to "normal" again. I think we are as close to being back to normal as we'll ever get but the sacrifice is that I know things will never be 100% the same again and I don't trust him 109% anymore. I haven't gone down the route of checking his phone or emails since as I don't want his mistake to turn into my problem.
He knows that if anything remotely similar ever happened again there's be no questions asked, he'd be out the door. I am quite a string person and even if it would break my heart, I would follow through with this ("fool me once, shame on you. Fool me twice, shame on me").
Once the shock has subsided (and I really do recommend you get him to move out whilst you process this), you need to consider whether you can cope with feeling betrayed for a long time afterwards (it's been a year and for me it still hurts almost as much as it did when I first found out). I know I feel angry when I consider that both of them got away scot-free with what they did (if I had reported them they would've both been out of a job), whilst I appear to be the only one who has suffered/is still suffering and I'm the innocent party!
I know I will never trust DH 100% again. He didn't go to his Christmas party, as it happens she also avoids school functions which are not compulsory. She is not married, so I never had any scope for turning her life upside down as she did mine. But I did inform her in my email that we had lost friends over what they had done, that my 2-y-o DD had (temporarily at least) lost her Daddy, and our families were devastated. I was civil in my email and only ever sent the 1 message, I think it's better to retain some dignity (if only to avoid confirming I am the mad old battle axe that DH has no doubt made me out to be!).
So in my experience things have improved. But I have had to accept things will never be the same, I will never 100% trust him again and the pain may never go away. Ask yourself if this were true for you also, would you be able to live like that? I'll be honest there are days when I feel I can't. Thankfully in your case the OW lives too far for them to meet up so you don't have that worry.
Once you feel able, make some changes in your life. Go out more, see your friends once a week (and let him deal with DCs). Take up a new hobby, join the gym, it's cliched but not only will it give you something else to focus on, it will show him you are a confident, self-sufficient woman who has plenty to offer (if not him, then to those around you). And if the worst ever did happen again, you know you'd have a life for yourself outside the marriage which would make it easier to walk away.
Sorry for the long post, I wish you all the best, I know where you are right now and wouldn't wish it on my worst enemy. xx