I am sympathetic to your plight OP, really, I am. Here is the part where I sound like an asshole. This is really more of a relationship issue than it is to do with the specific philosophy of Harm Reduction. It would be like moving a mountain for us to tell you precisely what is going on with your chick is up to and even if we moved said mountain, what would you have to show for it. You could certainly "tell them so", but even that wouldn't really have a positive impact on anyone's life in a significant way.
If I may play Montel Williams for a brief moment, what you are lacking in your relationship is honesty. How do I know this? Well, if you had a truly open and honest relationship, then you wouldn't be asking a litany of cyber-fiends to play Sherlock to your Watson. If there is no honesty, tell them to kick rocks. That's it. If they're fucked up and they don't want to tell you about it...
CONSEQUENCES
Dating liars will ruin your life. I am a reformed liar myself and I've done terrible things to the emotional health of women that I thought I loved. Don't stand for it. If they are doing wacky, crazy shit as if they're high on Meth, call them on it. Don't act like a moron or like everything is okay. It will only be harder for you to confront them down the road if you don't do it now.
Closed.