This is really useful, thank you.
I guess my view is muddied as I have so many 'experiences' to draw on personally. My father was psychologically abusive to my mother (and he was a drunk) and she was going to leave him when she fell pregnant with me, so she stayed another 2 years before eventually having an affair and leaving with her affair partner (meaning she left us, me and my older sister, with my dad). She told us about this as kids (zero filter for what was appropriate for us to know at what age), meaning I carried a lot of guilt that she suffered those extra two years just because of me. So the guilt thing I get. Can't for the actual life of me think why, if you did stay together 'for the children', you'd ever tell them that unless you wanted to fuck them up. No way I'd ever frame it that way to them (or indeed anyone else).
However, the fact they did eventually separate means I got to experience the 'joys' of a broken home, moving between homes, missing my mum and/or missing my dad, dealing with their continued animosity and poor co-parenting, and then step-parents and ultimately a blended family as my dad moved in my stepmum and stepsister, and went on to have my half-brother.
Now we are adults we all get on well, and credit to my stepmum she did put a stop to my dad's drinking which made him a much better parent and person.
But it was not at all plain sailing, I found the broken home aspect really difficult, the torn loyalties and a lack of feeling of belonging and (I realise belatedly) an underlying sense that nothing was safe or reliable, everything was contingent, people could just leave - which has followed me through life and given me maladaptive attachment behaviour.
I found my dad's difficult relationship with my StepSis frightening (and I'm sure it was very damaging to her, although as I say all good relationships now, he walked her down the aisle at her wedding); I found my half-brother being treated so differently in the home to me and my sister difficult (still do in some ways).
Basically, my experience of relationship breakdown and what comes after is not as it is straightforwardly painted 'it's better for the children than being exposed to their parents' unhappiness'. Happiness, for the parents or the children, is no more guaranteed after a separation than before it IME. It all depends on how you go about things (and cruel, or otherwise, fate to some extent). However, I also have the other side (knowing my mum 'stayed for you kids' gave me the guilt, and watching my dad and stepmum's difficult relationship (and my mothers' series of subsequent abusive relationships) was hard so I appreciate that 'staying for the kids' won't result in happy kids if you can't at least approximate a functional healthy working relationship for them.
The one that bugs me is 'you're not modelling a healthy relationship' though - if I broke up with my DP, I would NO WAY be having a relationship with a man ever again (both because I suspect a majority of them are quite selfish, because I wouldn't expose my kids to the risks of a blended family, and because I recognise that I myself have a lot of maladaptive attachment behaviours which make it difficult or impossible for me to form a healthy romantic attachment). So even if we separated, there is no guarantee of them getting a healthy relationship modelled to them - they might, conceivably, get to see a single woman being happier, but that would be it. So the idea that by staying I am depriving them of a healthy model they could otherwise have is stupid really.
This is why i was interested in the stories of the people who've actually done 'staying for the kids', from the parents' perspective rather than the kids' (though I of course appreciate the stories of those affected as children, but i have heard them before on many of the same threads where women are contemplating this path). I have a variety of experiences from the kids-eye-view that complicate rather than inform my thinking - I was hoping for a perspective of different versions of future me, and while you get a lot of the 'I left my partner, kids are fine, I'm living my best life now' type posters, you rarely hear from those who stayed 'for the kids' and subsequently broke up when the kids were adults, either positively or negatively.