I have just left my husband under very similar circumstances.
Please allow me to give you some advice: tell people in your life what is going on. You NEED to stop this from being a horrid little secret. You need support. I had stopped seeing friends as I was just so low and had no good news to talk about. I started telling people at work, and have been astounded at the care and kindness I have had from people, even those who have a dragon-ish reputation.
Secondly, you need to get some control here. You are within your rights to say clearly and calmly that he cannot take the children in the car. In fact, please let me tell you - that is putting them in harms way. Do not allow this to happen.
I don't mean to guilt trip you, but it's what got me in the end- your children are picking up on every second of this. They would be better off living in a shoebox wearing bin bags than thinking this is how relationships work.
I decided to leave, and then stayed, and changed my mind again and again, because really my dh is very unwell. However, his risk taking behaviour never got better, so I couldn't manage it. That orocess of taking time to decide has made it easy to know this is the right decision. What I'm trying to say is, take your time. This is a process, and you will not be able to make a decision overnight.
If and when you do leave, prepare for him to become more unwell. There is nothing you can do about this. My dh attempted suicide yesterday. I am so pleased my little boy did not see the fallout, we are safely staying with my family.
Please put yourself and you children first. Hope all is ok for you this weekend. Oh, and make threads on mumsnet. I have had a couple over the last two years, and found them massively helpful even if I didn't act on the advice straight away.