Sadly, I have experience with this too. If you smell trouble, document everything. Document when you talk to your landlord, when you talk to the rental association, when you have conversations with your roommate, when incidents happen, and don't be afraid to use law enforcement to help you out. If anything ever happens that leads to the courts getting involved, be it criminal or small claims, you'll at least have a timeline of how you attempted to deal with the problem.
Roommates are temporary, trauma is forever!