OP, I'm sorry you are in so much pain.
But - why are you taking all the blame for the marriage ending? HE ended it, saying you are not the woman he fell in love with? What is that woman? One who did everything around the house so he didn't have to do anything? One who shouldered all the 'wifework', childcare, housework... so he had a lovely cushy life? And when he is expected to actually do something, blames you?
He doesn't come across well in your posts. No-one in an equal partnership should be expected to bend over backwards to please a partner, take on all the work, be all things to him.
Stop blaming yourself, and get Team DearSomeone together.
Get him out - he wants to leave, don't listen to bullshit about how he'll love you as the mother of his children - not what you need or want.
Get legal advice.
Get yourself safe and look after the most important things - you, and your children.
He can look after himself for once.
The InLaws - can wait. They will not be on your team, they will be on his. In the future you can rekindle a relationship - for now, do not lean on them.