As you can see, addiction is a progressive disease. Think about what he said, about being afraid social services might get involved. This is actually a valid concern. Your children ARE in danger. And if SS does find out about all of this, they will see you as a danger to them, too, because you are allowing all of this.
You have to understand: They will not care how many times you've begged and pleaded with your husband to get help. They will deem you guilty of failure to protect your children and they will take your children from both of you.
Now, as for you losing your cool and punching him- that's really no surprise. He's caused so much chaos and upheaval in your life, of course you're angry. But watch it. Because it's entirely possible that if you do this again you could wind up with a restraining order against you. And when a parent is deemed a danger to the other parent, it is assumed they will also be a danger to the kids. You could end up with a permanent criminal record and no access to your children. Meanwhile, he'll have full custody and will be driving them around drunk to his dealer's house.
And honestly, that's not even the worst case scenario.
Please, see this situation for what it is and take the appropriate action to protect yourself and your children.