I have mentioned to him in the past that I have documentation that totally supports my claim that he is an active drug user (which I do)... All he ever tells me is that I am just a liable as he is because I knew about it, and I did nothing...so I'm basically an accomplice.
This attitude would worry me. He is right, you DO know about it. My worry would be that if he ever did get right, move on, remarry etc. Would these be grounds for a custody battle in the future?
You are doing the right thing by making sure it's supervised. Have you talked with your case worker about this and how to handle it? At least if child support knew of the situation, you would be covered for future battles if he would ever try to come back on you.