Well I've just read the whole thread OP, and was relieved to see a couple of pages ago a little spark from you, because you sound like a little kicked kitten, and my heart goes out to you.
So many of us, hell - way too many of us have been where you are now, and you've got some lovely support on here.
You naturally love your H, but I'll be honest OP, I don't like him one little bit. No decent man would have an affair. Many not too decent men would draw the line at cheating on a pregnant wife. You two got together, had kids and of course you changed! Being a mum as you know is a slog, rewarding yes, but bloody hard work. You seriously think that if you'd washed a few pots up, before his lordship returned home, he'd be happy??
There's an OW here, the thread reeks of it. He hasn't the balls to confess, so like my ex, and countless other spineless twunts, he's playing the 'you've changed..I want the girl I married back...I love you but I'm not in love with you' card. Thus, he is absolved of any blame, and you run around beating yourself up, blaming yourself and wishing you could turn the clock back and 'do it all better.'
I did that, took the blame, jumped through hoops, nearly had a breakdown believing it was me who was a rubbish wife, and took all the guilt for a dad leaving three gorgeous kids. Then I found out about his long affair...
Get angry. Take control. See a solicitor. Let him see that this won't break you. It won't, I promise you it won't.
You are a mum, a good mum. You have been gaslighted by a man who has a plan, and right now you don't know the whole truth. What you do know is that he wants out, so let him go. Let him go, seek legal advice, lean on RL support (but not too much on his family), take it a day, an hour, a minute at a time. Early days, hold our hand if you need to. x