His drug problem is his to resolve, but sadly it turns into a family disease. You can't help him but you can keep your children safe and decide what you will and what you will not tolerate. You don't have to decide today, maybe make a plan in case things don't work out.
It might be a good idea to protect your valuables and separate your finances from his. You will need that money to support your children and yourself, and sadly, loss of money and valuables is common in situations like yours.
Something that has helped many of us is meetings of Al-anon, Nar-anon or CoDA, three similar fellowships that are about US and that help us regain our balance and learn to live healthy lives again. Maybe check your area and give them a try, you have nothing to lose and everything to gain.
Hugs