Feel free to be blunt with what you want to say, I promise I don't get offended easily.
It's not that... I have been on the other side of your problem. I was using, scaring the shit out of my wife and lying about it right to her face. It was obvious i had a problem... She was scrambling to do whatever she could to help me.
But the reality was there wasn't much she could do or say. I had to come to terms with my problem. I had to decide I wanted to stop. I had to be the one to make myself stop.
The only thing my wife could do was be there for me... And at my worst, the best way she was able to be there for me, was by stepping back and letting things fall into place. She told me she knew I had a problem. She said she loved me and that she would be there for me. But she also made it clear that she wouldn't put up with it forever... She knew I wouldn't get better over night, she knew it would probably get worse before it got better.
Luckily I was able to get myself turned around and better... Before she got completely fed up and left.
Of course, I'm still an addict and I still struggle, but at this particular point things were BAD and she was just realising I was using. I had been for years, she just didn't know until it got bad.
I just don't know what to say to you. You must realize this guy is an addict. Most of us addicts don't suddenly get clean and stay clean forever. He will likely struggle with addiction his whole life. I know I will. Even when I'm clean, I'm still struggling.
I think you both need to get past the point of his denial. That is not easy. The hardest part for me was that at first my wife talked down to me and tried to control me. This just made me resent her and lie to her more. I'm not sure how your relationship is, but he is probably ashamed to admit anything to you. He probably doesn't want you to worry. He may not fully realise just how bad his problem is getting yet.
Addiction is horrible. I'm sorry you have to go through this.