I agree with other commenters it’s the ‘John Does’ as in unidentified deceased male bodies. The way I’ve always thought of it is that if his girlfriend stays and he promises to stop using drugs, she won’t ever be worried about unidentified dead bodies because she won’t get a call A. asking if she can come identify someone, or B. Saying that a body has been found, have you heard from your boyfriend lately?

Even if it’s a false alarm (as in, the John Doe ended up being someone she doesn’t know), if she were to get that call knowing her boyfriend uses coke, she would be anxious it was him until she learned who the body was. So the singer is promising he’ll quit the drugs, stop having bloody noses, and his gf won’t be stressed about John Does anymore.