Mapam, you're doing so well. I always agree with AF's post, but she's hit the bullseye with her response about your ex being a manchild.
People used to say to me that I had 5 kids, not four. I used to mother my ex, I think that's part of why we drifted apart, he was happy to be treated and cared for like a child - I was happy to do it. So I take part of the blame for that. But it doesn't excuse their behaviour, not one iota.
My ex has a huge sense of self-entitlement, unbelievably so. Yours probably has the same - it's because they've always had someone, parents, us, whoever, to pick up the pieces, the put the blame and responsibility on.
Be prepared for your ex to flounder because you've taken away his security blanket, his adoring audience. Like a child, he will probably sulk and act up and blame you for everything. (The engagement ring incident is a textbook example). He'll spit his dummy out. Let him. Ignore, ignore and then ignore. Not your problem anymore. Right up until almost the end, I continued cooking, cleaning, ironing and fussing over a man(child) who had told me repeatedly he didn't love me anymore. But I'd always done far far more than my share about the home, and it was very hard to stop. I had to learn how to stop doing stuff for him. But stop I did.
You and the kids are all that matters. He has chosen this - even if he hasn't had the guts to actually make the break, believe me 100% - he wanted this - that's why you got to breaking point - he drove you there. My ex did the same. So whatever is ahead for him - is for him. Don't worry about him, about how he's coping. He has a lot of growing up to do - let him do it. You have a lot of healing and self nuturing to do - so focus on that.