If he tests positive, he’s using it.

Many alcoholics and drug addicts are functioning and hold jobs. But it’s all good until tragedies hit: they drive drunk or high or drugged up with kids in the car and get into accident or set house on fire because they fell asleep high/drunk etc

You are only fully functioning when you have no mind altering substances in you.

I’d honestly go through the court system. You don’t need to be divorced to establish visitations/child support, he will need to attend NA and test periodically etc Keep record of him testing positive and acting irrational etc