I've read through the OPs posts and if this is a post her stbxh or ow find, I want them to know that this level of cruelty and decit, makes them both perfect for one another. Pair of cunts. They can gaslight themselves into thinking its a great big love affair but ultimately you've both destroyed a good person, a person who has 3 children to care for, sanity. And no, OW doesn't owe OP or her DC anything, but supporting a man who lies, gaslights and purposely fucks up the mental wellbeing of his children's main care giver makes her complicit in cuntery.
As for him? I hope he loses his hair, teeth and gains weight as rapidly as he manages to spin a yarn.
OP I hope you listen to the advice the wonderful and strong women who've been in your situation will undoubtedly leave you, these are the women who've got experience and shown courage and become wonderful single parent families without some utter prick dragging them down. These women have a wealth of knowledge and advice, listen and trust them.
You have your beautiful dc, your health, supportive family and ex mil, you're not going to be poor.
Enjoy your babies, enjoy the freedom of no weak brained pleb of a man who isn't going to make you feel like a crazy woman anymore, take him for every single fucking penny.
And the only advice I can give having been a single mum myself in different circumstances, don't spoil your DC to compensate for a shitty dad, I over did everything because my DC dad didn't do anything for birthdays/Xmas and i didn't need to, he tells me now he's adult that my love and strength was quite enough and he wished I'd not struggled as much as I did, he'd have been happier with me home as opposed to smashing the overtime, that's all I've got.
All the luck in the world hen, I think you'll be amazing!