Originally Posted by
FireSprite 
What you are doing though, IMO, is tipping your hand and helping him figure out better ways to lie/mislead you in the future whenever he gets caught again. Not if. When.
This is so true. When "we" (those who love addicts) start playing this game, we are engaging at their level, and actually feeding their addiction. They begin to focus on "beating" us, and when they are successful in the deception, they get a dopamine surge...just like when they use. As long as they can focus on fooling us, they don't need to look at their own behavior.
This is what I see: he is addicted to drugs...and you are addicted to him.
I don't mean this harshly, but I urge you to do some reading about detachment, and also to attend an AlAnon meeting. I think it will help ease some of your distress.