Newcomer...

I broke up with my boyfriend not so long ago. He continues to call, and I have to deal with him to a point because we have some financial issues that prevent me from cutting ties altogether.
He started a new job today. Turns out he needs to take a drug test. He knew that. I was with him when he interviewed for the job, and he knew he needed to pass the drug test. So he calls tonight all upset because he says he smoked marijuana over the weekend. Now, I know from experience that this is just about the only drug he does NOT generally enjoy. In the entire time we were together, he smoked marijuana once. Not that this should be an accomplishment, but compared to everything else he was doing, I just was not worried about it. I also realize he's probably lying, and for whatever reason, feels that I'll be more sympathetic if he smoked marijuana than snorting whatever pill he managed to get his hands on to crush up.
So, he tells me he's on his way to GNC to get some cleansing kit so he can pass the test. I remind him that if he has money to pay for the kit, then he should probably pay his half of our joint bill that is due by Wed. He then says that he has no money and will have to steal the kit.
Now, aside from me, and a few select family members, I have never known him to steal - particularly shoplift. I know its the cycle of addiction and that he'll keep stealing more and more as he becomes more desperate and people stop giving him money. I also don't know if this was just him trying to get me to buy the kit from him - and, to his disappointment, there is absolutely no chance of that happening.
What I can't figure out is why this is bothering me. For weeks he's been calling, I've been maintaining conversation when I've needed to to ensure that bills get paid and to sort out financial stuff we have to work out. No matter how high or drunk he has been when he's called, I've been able to hang up the phone and move on to what I was doing before he called. I don't know what it is about THIS particular call that is bothering me so much. There is nothing I can do about it. If he gets caught, maybe it will be good for him. He could use some consequences these days....
Then again, if he doesn't work, if he doesn't pass this drug test and loses this job, he can't pay the bills that need to be paid. Since the bills are in both of our names, I am just as liable as he is - meaning that if he doesn't pay his half, I am responsible for the whole thing. There is no legal way around it - I've tried. Maybe that is why this is bothering me so much more than it should. I guess in some way I'm feeling that it does affect me.
I have felt this anxious since I left him. I am trying to just focus on the work that I need to get done, but can't. Now, if I could just figure out why that is, maybe I'd be able to accomplish something...