When I was married to ah, I could see the signs he was thinking of using drugs before he even realized he was thinking of it. For ex, he would get chipper, start to help around house more, his whole mood would change. He also had a definite pattern.
Have you noticed if his calm periods are getting longer? Or his using periods growing shorter if so this is a good sign. Most addicts eventually quit by themselves, when the results of using get worst then if they stayed clean. Another words they see something in life they want more then the results from using or drinking.

katrinka, you are right, now i am that balancing the fine line of disengagement and letting him know i am onto him. today i opted for non dramatic conversation......he was shocked that i seem to know him better than he knows himself. i also did not let him tell his "story", i just reinforced that no matter what he tried to tell me..... if it was outside the acceptable agreed upon boundaries, the consequences stood.