oh, in case you wanted the best answer, stay the fuck out of it, i wouldn't even call the cops, best case, cops actually get some thing done, hes goes to prison, and she gets some rehab, gets out of rehab starts doing drugs again and really isn't better off, worse case, some how he finds out you called the cops and kills you.
and he doesn't even have to know it, all he has to do is think it, ive none a enough meth addicts to know they don't need proof to think some one called the cops, all they need to know is some one doesn't like what there doing and cops showed up. and the last thing you want is some drug drama on your porch. and from what you said so far this guy knows you. and knows you don't approve of him, and if the cops come knocking on his door saying some one reported some thing of another, good chance he will think it was you.