Dear ontheedge you have done brilliantly to get thus far; it is only eight months since your husband turned your whole life upside down. Christmas must have been full of echoes of the past but with the company of your children it is not surprising that you collapsed after they left. It will pass; you are grieving and grief hits hard and unexpectedly, but eventually returns less frequently until one day you realise you don't care
Your husband is a liar and a cheat, and above all, utterly crass, renting in the same village and attempting to rejoin your social circle; he no doubt thinks he is no end of a dog. Don't allow yourself to be driven out unless you really want to leave, but don't underestimate his new woman. Unfortunately, social life is geared to couples and single women pay the price, not cheating husbands.
For now, just concentrate on getting through each day; cry in the shower, and make it to your work if you can. See your friends but guard your tongue. You will find who your real friends are. Be as dignified as you can, some comfort in the dark hours of the night.(I wasn't always.)
I was 41 when it happened to me, it was not a happy marriage, a complicated situation and not a clean break. I reluctantly followed my husband, at his persuasion after a trial separation, to his new job; I still don't understand why he wanted us as he virtually abandoned us once there. I knew no-one but soon learned everyone knew him and also his 'wife', the woman he was living with who had adopted his name. I had children of primary age, a new job, and suddenly a large mortgage to meet which kept me going, but I know the despair you feel.
It will get better and you ^will6 find the strength to cope, but it will be hard at present and desperately unfair.