Sparklerach
I'm so terrible sorry for all that you are dealing with at the moment and that the man you married has turned into a cruel, cowardly creep.
I am supposed to be doing something else now but was so so so livid on your behalf, I had to stop to post.
I can't believe it but I feel like I have lived your life before you (just one year in advance). I will pm you as the details will out me but there is no doubt in my mind that he has an ow and probably has done for sometime. When my DH left 'because we weren't compatible' and wanted to be best friends, was around all the time and still depended on me for all kinds of support, I thought there was no way he had an OW (even though the lovely ladies on here did give me a heads up!).
This is what you need to do. Search for evidence (his mobile bills are the best bet but card statements good also). Ideally confront him when you have evidence (he will deny anyway). Although even if you can't prove OW, I would still do the following.
Ask to meet him for a chat out (pub or somewhere), for your own self esteem pick somewhere nice and turn up looking your best. Be calm, cold, aloof and contemptuous.
Say that given his behaviour in recent times and most particularly the way he has dealt with leaving (email, being away, changing bank details, lack of consideration for the children etc) means that (amend to suit):-
He is not the man you thought he was
He is weak and cowardly
His behaviour has been appalling for some time but this takes the biscuit
It was his responsibility (jointly) to make your marriage work and create a family for your children
He was certainly not the perfect husband but you didn't give up on him/your marriage at the first sign of difficulty
He is not your friend, as you wouldn't dream of being friends with someone like that
You are not interested in reconciliation and you have no interest in being married to a man who would act like that
You have no intention of being 'friends' with him (although you hope in time to be friendly for the children's sake)
You need time to recover from the breakdown of your marriage
You will not be his friend or support system any more (he lost that when he treated his friend like dirt)
You will only speak to him regarding the children/practicalities and email/text is better for the first while
He left your family home and it is now not his home. He needs to give the keys back.
You will hand the children over to him at the doorstep (even better if you can arrange for someone else to do so)
Even if he doesn't have a place to bring them he needs to take them out for his weekend contact.
He can see them/do bed time one evening a week (I suggest you go out this time - even if only for a run/swim or I sometimes went for a pizza/glass of wine with a magazine) - this is to enable you to recover from the shock and not punish him.
You are justified in doing this as he left your marriage and family home without discussing his unhappiness/counciling etc. You need to take control back.
Whatever happens, this will allow you to keep your dignity. If he has an OW, you will be so glad you didn't allow yourself to be treated badly for longer. This might shock him out of his little fantasy. He will not be expecting it. If he has no intention of coming back, it will help you to deal with it so much better by detaching from him and not subjecting yourself to his company (it's impossible to get over a relationship when you constantly see, are drawn in by someone).
PM me any time. I know it feels like hell now and probably physically painful but I promise you, it will get better and you will get through this. Just take it hour by hour. You need to find some coping techniques fast regarding, putting thoughts in a locked box and refusing to go there (sounds impossible I know but you will manage).
You are in my thoughts. X
PS all the awful things he has been saying about you and your relationship are fabricated or at least highly exaggerated to allow him to justify what he is doing.