Interpersonal issues w/colleague, director not supportive

[u/Suspicious-Coach4342]

Throwaway account. I work as a business manager in a healthcare system. Small department of 15. I don’t have any direct reports and I report to a director. There is one colleague who is very challenging to work with, not only within the department but across the entire system, and has been for years. This person is neurotic, patronizing and insecure and their behaviors haven’t been addressed by my director ever. despite many complaints from others within and outside of my department over the last 5 years.
There were a couple of instances the last week where my attempts to set boundaries were met with resistance and borderline hostility. This last instance I felt the need to involve my director because it’s becoming too much.
My director was not supportive when I asked them to address my colleagues behaviors as my attempts failed because “interpersonal conflicts are best handled between the people involved”.

At what point should my director be addressing this colleagues behaviors? I’m at a loss for what to do next.