It's tough when kids are involved, but they're not stupid, and will probably know all is not right.
I went through a similar situation to where you are now nigh on twenty years ago, and spent two or three years trying to fix something which was obviously broken. All you can do is try.
For many people, just getting to that point makes both sides realise they have more to lose by splitting up than they have to gain, and they manage to turn it round, but equally, if staying in a relationship is making everyone miserable, then there does come a point where it's better to call it a day.
All I can really say is that, if it comes to it, then there is life after a long-term relationship breaks up, and, despite financial hardships, it may well be a better life. Before you get to that point, I would recommend something like
www.relate.org.uk though. Sometimes having everything out in front of a stranger, warts and all, can make people realise that they are closer than what they want to admit. I've seen mates go to relate in absolute turmoil and come out of it stronger.
Basically this means I'm on the fence