When my dad left my mother and me, she had never worked. She didn't have a driver's license or a car and was totally dependent on my dad. She made it work. She got a job in the shoe repair department of a department store and rode the bus. She did that for years until she saved enough to buy an old car. She continued getting better jobs and better cars through the years and she retired from a national company about 8 years ago with a nice pension.
That said, yes, it is scary, but you can make it if you are determined enough. Your kids will be able to get jobs soon to help out. Yes, it will be hard, but if your husband just decided to leave one day (as he has threatened to do), what would you do then? What if he has a heart attack or stroke? What if he dies? I know I sound harsh, but no one should be totally dependent on another person. You are not responsible for your husband, he is. If he refuses to make a doctor's appointment for himself, then why should you? Instead of taking such care of him, why not put that effort into taking care of yourself and your kids and let him do whatever he decides to do. What he does is out of your control, but you can start now making sure that you and the kids will be okay regardless of what he does.