Gem…
Bama nailed it on the head.
He will play you and everybody else as long as he can. Make some ground rules, and stick to them.
I am so sorry about the kids though.
It would be what he needs to let him drop hard. But his kids don’t deserve to fall with him. Maybe he will get popped one more time for possession, sale, whatever, and the kids will be removed from his care. As an active junkie, he might appreciate not having to be bothered with feeding, clothing and educating them.
There is no good solution to this one. Stay close to the kids. Buy them cloths as you can afford them. Keep the lights on if you can, You are right to give him nothing in the way of spending money. You know how that goes.
Again, I am sorry for you. But I am mostly sorry for his kids.

May this power greater than ourselves smile upon you
Richard