"Maybe leaving is what he needs me to do for him to get better... "
It won't do a thing for him one way or another. He has a progressive disease that has no cure. If he stops using and gets into a strong recovery program for life, he has about a 10% chance of staying clean for life. If he doesn't choose recovery, the disease will get worse and worse, like an out of control freight train.
Leaving would be done for you and your children. Your children should be your priorty, they should never live in a house where addiction is present. They hear and see everything and will carry their childhood into adulthood. They are watching you enable him, they are watching you put on your rose colored glasses again and again. They will remember, as an adult they will affected by their childhood enviorment.
I am not telling you what to do, you are an adult it is your life, your choices, meetings will help. Read all the stickeys at the top of this forum, do research on addiction and children of addicts...knowledge is power.
I wish you the best.