Thing is aleC, your ex wasn't thinking with his head when he dropped the bomb that blew your family apart. Like my ex, he was so full of his new life, his mind so full of all the new possibilities of life with OW, that he refused to see what he was throwing away. The haste with which your ex rushed through leaving was breathtaking. One of your early posts said something like "he wants to tell the kids', then next post 'he's told the kids'. We were all taken aback by the speed, which naturally left you reeling.
You could see, just like I could, that he was throwing something away that could possibly be fixed. But like mine, your ex had spent a lot of time deciding and planning his new future. That was the bit that I found most hurtful, that I, the other 50% of the marriage, had no say in the future. He alone made up his mind, and it was presented as a done deal.
I got an email about 3 months after he left, full of remorse. And I too cried, because I could see that he was waking up to what he'd lost. Most of my tears were of frustration and anger that the bloody fool hadn't realised what he was losing until it was too late. And it really was, by that time, too late. The thought of having him back crossed my mind, but only fleetingly, because he had caused too much pain, I knew I would never trust him again, and actually by that point he had killed any feelings I had for him, but I still thought, 'you bloody fool, why didn't you realise this at the time.'
Of course life with OW isn't a bed of roses. Illicit trysts with OW, romantic dinners etc., are one thing, living in reality, with all the day to day drudge life throws at us is quite another. He's living a different life to the one he envisaged with her. So be it. He made his bed, with her, he can lay in it.
Just hang in there, and try to focus on you and the kids. You are doing very well and you will get through this my love. It is still early days, you are dealing with financial stuff that you didn't envisage, at a time when you should be licking your wounds.
I got through similar, and so will you.
We're all here, rooting for you and admiring you.