"I must've turned him to drugs, and now if he kills himself it's my fault"
Being codependent has NOTHING to do with his choices and his addictions. You did NOT cause his issues, if he hurts himself it is NOT your fault.
You said he has had problems through your whole relationship...so why again is this your fault? I am guessing he probably had problems before your relationship since you mentioned he cannot handle stress? How is the fact he can't handle stress your fault? You cannot shelter him from stress in his life, thats a FACT of life. He has two children he isn't taking care of, how could you have pushed him too much? His child was sick in the hospital and he went off to escape leaving you with it all? That is not normal, a partner and a parent is present in the time of need, that is part of being an adult.
HE has chosen not to get help. He didn't take your car to go to rehab, he took your car to go do drugs. Leaving his children and mother of his children with NO transportation and having to take buses to get FOOD. Are you seriously blaming yourself for any of this?? He chose drugs over food for his family.
I can't give much advice about relationships with addicts, I am here more for my brother and family full of addicts, but I can say you definitely need to step back and take care of yourself and your children and let him make the decisions he is going to make. Keep yourselves safe and out of that mess....giving him 'help' just turns into you having to struggle to take care of your kids and yourself.
I am sure it has been said before on your previous post, but read the stickies at the top of this forum, find someone or a group to talk to (a therapist/counselor, nar anon, al anon, whatever works best for you). Get help for yourself so that you can be happy and help your children through not having a present father.
I am codependent. This doesn't mean I caused my brother to be a heroin addict, my mother or father to do what they do, etc. It just means that I am having to relearn how to be happy with myself, not anxious and worried about fixing, repairing others. The addicts in my life were going to do what they were going to do whether the codependent me was in their life or not. I just allowed myself to become a tool in their addiction, but I definitely did not cause it nor did you.
Deep breath, sending positive vibes your way.