i just think when does his mental health stop trumping ours ?
That'll be when you decide the time has come to prioritise the mental health of yourself and your children, which is an entirely responsible and appropriate thing to do.
He is not going to walk away simply because of a sudden epiphany which makes him comprehend the toll his state has on his family, and you are under no obligation whatsoever to just tolerate whatever happens between now and him getting better, whenever that arbitrary point in time might arrive, so if it really is at the point where you believe you and your children need to be away from him either temporarily or permanently, then that's a decision you will have to take because he's not going to be forthcoming with it in his state.
You can't make him better, so there really isn't any point in hanging around at the stage where it is making you and/or your children ill as well. You can't sacrifice your own mental wellbeing just because your partner is ill, and I say that as someone who has lived with mental illness my entire adult life and also left a very long term relationship largely because of the consequences.
People inevitably want to support an unwell partner, well the decent ones do at least, but there is invariably a point where that help and support becomes inconsequential, and the only purpose it serves is to diminish the life and health of the people trying to provide it.