All I can say is this a healthy environment for the children? From your post it doesn't sound like it. What are gaining from this relationship? What example is he setting for his children? He is and will be their idol.
I can relate as my xah started smoking when he was 20. We married when he was 25. He was still smoking. We had a baby and he refused to stop He had to get high before the park, before watching a movie, before a trip...always the focus was him getting high in the garage while we waited. He would come out all spaced out and no fun to talk too. Meanwhile, I was responsible for taking care of my son. I remember going to the grocery store and coming home and it reeked. He had my son watch cartoons while he went and smoked weed. GROSS! Maybe your AH isn't doing it at home, but it still sounds like it is affecting your life and family.
My x continued to cocaine and abandoned us.
I suggest weighing out what are the consequences if you stay. My x's mom stayed with an alcoholic for 20 years. My x became and did exactly what his father became, but with drugs...exactly. She stayed because of religion, fear and the idea that "this was her family"