Debutante, so many couples are in this situation and they're both miserable. If, as you write, he is a "good, honest, hardworking man", he wouldn't be taking you for granted and gratifying solely his own needs. I married a persona that disappeared at the 5 year point. I stuck it out in spite of his nasty remarks, flirting with a neighbour and on a few occasions doing deliberately dangerous things that would have looked like accidents had he been successful, but which would have totally harmed, if not killed me.
One thing I would say, he may turn seriously hostile once separation begins. The solicitor I did hire told me there's always one in a divorce that asks, "who is that person?". That was before that solicitor began to put into play tactics that would have forced the sale of the house to pay their excess fees. I ditched the solicitor, became a litigant in person and the agreement as it stands is in my favour because he got up to some financial irregularities and I had all the proof. If the house had been sold, I'd have lost any profit paying private rent.
I totally understand your concern about leaving something for your children, particularly as one has ill-health. I also understand those that have said think about your happiness first. It is a balance you'll find.
Living together but apart would possibly work if you could sell the house and buy one with an annexe. Even then, you would still have to have dealings with that person you may be better off without.