Huuuuge hugs OP! Assuming it is a partnership-type level promotion, firms will always put more people into "the funnel" with 2 years to go than will make the grade. That in itself is part of the process. Everyone on the path will receive mentoring & feedback & fine-tuned goals. He won't have been without input until last week!
These days, most firms want partners who are capable of managing the balance - of having an interest outside of work (doesn't hurt if it's high end & client schmoozable like fine art, or horse-racing, or yachting; but equally doesn't matter if it's avidly supporting darts or snooker or your childhood town football team; or taking your kid to comic-con or warhammer conventions!)
They also need people who can HANDLE the stresses & ups & downs that come with partnership, AND manage a family & social life.
It sounds like DH was probably an outlier/old school pick in the process anyway & not making selection certainly doesn't have anything to do with your wobbles last week! Tell him if he'd like to chop you in for a stepford wife with a texas blow dry that would be fine tho - you can take your 50% and EOW and he can crack on, as you'd be giving up less (change of lifestyle than he would in a split anyway.
I have a friend who didn't make partnership & split from his wife around that time. He now acknowledges it was never really his bag, but she was very strivey & it was important to her. His career has been anything but a flop since - just a different focus (having left Big 4). Sure he might take home 1/3 of what a partner does, but it's hardly peanuts. And he now has children & time to devote to them at weekends & enjoy life, as well as a decent career.
You clearly ideally need to talk to a counsellor together, as this is a big life pivot. He could get his house in order & readjust his priorities. Or he could continue to blame you & drive an even bigger wedge in - in which case you & the children would be far better off out of there.
I suspect that follow up guidance is available from his firm for everyone who doesn't 'make it'...doubt he'll mention it but maybe you could ask as part of a 'what's next?' discussion? You've put even more into the last 15 years (emotionally) than he has. You need to work together to figure out a mutually rewarding refocus...
Or your alternative will be very clear. Good luck 