OP, I understand the disruption a divorce can cause but as others have said, you are making such arrangement acceptable for your children, which can make your children miserable for years to come, even when they are on their own.
But if you are decided to stay, you need to start making a life on your own, and don’t sacrifice everything to keep the environment the same for your eldest. Don’t model your life around that, as things can change.
With regards to building a life... it is never too late. Important thing to mention is that you can build a new life but you shouldn’t aim to get the life you had before all this. Accept the loses, salvage what you can and start again. It may be a wonderful life, may be better than before, but it will not be the same because your circumstances are different nowadays.
I left my exH nearly 10 years ago, and have been raising DS on my own for most of that time. I’m not going to say it has been easy, far from it but these have been the best years of my life. I have been happier than ever before even with the knock backs and daily little struggles. Life becomes a wonderful thing once that you don’t have to live it “one day at a time.”
Having said that, I felt my life was gone at the time I made the decision to leave, but I didn’t leave straight away (I couldn’t), so I started rebuilding my life little by little: got a job (any job), saved for a car, got my own group of friends, saved enough money for eventualities, found my feet. It took me three years to put all my ducks in a row, I left when I was ready, strong enough to manage it and with a good number of friends that could support me through it. No regrets.
So, again, re build your life for you, but don’t model it on the idea that you and DH will be together, because at the end of the day, if things are that bad, he may leave you too.