"My question is, Do I have the legal right to keep my son from him while he is in the active state of drug use?"
Yes absolutely, but not without due process. You will need to present evidence of his abuse. Incidents of abuse in the presence of his son will be most compelling as will evidence from neutral third parties i.e. police reports.
It is possible supervised visits will be imposed. Of he'll be required to take drug tests as a condition for visitation.
I don't think you'll get very far with any of this without the help of a lawyer.
If you're successful in putting restrictions on his visitation, it's likely that he'll forgo visitations altogether. Oh wait, he's already forgoing visitation.