Many times, people will manipulate you by making a person feel guilty and unworthy--look for these messages, recognize them and disagree. Once you recognize their techniques, they have less power. Then they will either stop if you insist or take it to a new level of nastiness. Yes, a drug addiction or mental health issue could be causing the nastiness but if you are firm about it then if it is a drug or mental issue by telling them you won't put up with it--if they love you, they might eventually do what is best for them in the long run. It can be hard to know if it is a mental issue or you are just being used so don't be used. If it is a mental issue then you can be there for them when they show they are getting help (by their actions not their words!) Some people will use you up if you let them. Don't let them.