@jennyswoke Thank you for caring about a fellow human being who you obviously know quite well. You then have enough compassion left over to feel some concern for all those others who end up finding themselves in similar situations OP. I think that that makes you an extra special person jennyswoke because I am sure that your life will have it's own ups and downs, and so many of us these days just concern ourselves with our own problems, and feel that we can feel superficially sorry for others, but we don't actually have the energy left to have any real compassion for them - well that is what we tell ourselves anyway.
I have to admit to being very surprised by the number of posters having a go at you here OP, have we had a sudden heavy influx of men on the site, or just what is going on?
I ask because your opening post was lovely and caring in the way you were standing up for/feeling very bad for, a friend or acquaintance, who is a female with children (just like the people Mumsnett was established to represent), but who has a selfish arse as a partner.
So many of the PPs are behaving as if a "romantic" partnership is - and should be - only a business (and not even a moral) partnership. I don't believe that it should be a box ticking exercise with each person doing exactly the same amount of anything, whether that is earning the same amount of money as each other, working the same amount of hours on a paying job or a domestic one, or contracting that so many hours of M earning £XXX,00 per hour is equivalent to F caring for any and all children per every 3 hours, whilst also doing all the housework, shopping, cooking, nursing, and chauffeuring etc during each of those sets of 3 hours (figures loosely based on M working an 8 hour day).
There are so many other variables to take into account - far too many to be listed here - and those variables include financial considerations from both parties, physical and mental health pertaining to both parties, general needs and wants for both parties, but above all, the two most inportant things that any "romantic" partnership should, in fact, must have, and to be shared equally if the partnership is going to work survive, and thrive, is of course respect and love for each other. I think you probably agree with at least quite a lot of what I have said here Jennyswoke?
I firmly believe that the most unfair thing about the couple the OP is talking about, and the crux of the matter is that the poor lady seems to receive no respect from her partner, and very little - if any - real, unselfish, compassionate, love from him. If he had any of those feelings for his partner, he would see how much she is struggling, and therefore take a large amount of the physical hard work off her, and alleviate what I expect is an even harder, mental load. He can do some or all of the physical part by paying for domestic help if he wants, but he needs to step up immediately to at least halve her mental load, eg. involving himself in the actual mechanics of bringing up their children, and discussing them in positive and supportive ways with his partner, and he needs to spend a lot more time as a family man with his partner and children, and alot less time as a single man pratting around with his equally immature mates.