Hi Non,
I'm so sorry for what you're going through. My ex husband was also addicted to pills and was supplementing his prescription by buying extra off friends. His addiction progressed rapidly and he eventually moved on to street drugs. I definitely went right down with him- I completely lost myself trying to get the old him back. And I never did. I went absolutely insane dealing with his constant lies. I started drug testing him, but even when they came out positive he'd say they were defective. It was a miserable life.
If I could go back, I'd have worked on myself sooner, instead of always trying to fix him. I'm now very diligently working my own program, and have been for over a year. I've learned a lot about addiction, and a lot about enabling. I see now that I was just as sick as him.
I hope you will do your best to get out of his head. Stop trying to understand, because you never can. Stop believing that he doesn't see your point of view, because he most likely does. He knows he's out of control. He's just not ready to admit it yet. That's kind of bad news, by the way. He's not even at the first step yet.
Work on yourself. That's all you can do. Start setting boundaries and stick to them.
All the best.