Need advice

I’m 21 years old I’ve been with my children’s father since I was 16. We have two kids. A 2 year old and a 6 months old. He is a addict. He’s been a addict way before we got together and when we got together I though I could heal him. I thought I could save him and things did get better for awhile until they weren’t better anymore if not worse. We had our son and not long after that he would leave me at the house with his family (because we lived with them). He would stay gone for hours then come him higher than crap. We would get into arguments which would turn into violence. He’s died on me a few times which has traumatized me. Now he’s been in jail for a year due to his drug use and some bad choices. I had our daughter six months ago and he talks about getting out and doing good and us being a family (Because we are still together) but I’m not happy. I’m talking to this guy now and things are getting serious but I’m afraid my child’s father will overdose and kill himself if I leave him. I hate the fact that I gave my children a father who is a addict and might not be here one day because he cannot say no to drugs. I don’t like the thought of having to worry about him and if he’s going to die on me or even go get drugs and nodd out for hours which is super heart breaking but I also don’t like the thought of us not being together for my babies. I love him but it’s Been the same vicious cycle over and over again for almost 5 years. I just want to move on with my life and be happy but I’m afraid of the unknown.