I don't understand how my AH could get caught up into drugs again since he knows all the damage it causes (i.e. family).
Well, you don't understand it because you're looking at it rationally. If you look at it from his point of view, he wants to do whatever he wants without paying a price. And then when you or whoever hold him accountable, he's outraged.
I would assume the worst. I would assume he's using, and I would assume every time his lips are moving, he's lying.
Can you be in a relationship with someone that is an active addict too? Or is it just a partner in crime. She lost her young child to her hubby b/c of her drug problem.
I wouldn't consider it a relationship in the healthy, traditional sense. Sick attracts sick. And since they're not going to hold each other accountable for what they do, they're perfect together.