I’ve never seen a business, ethical, or religious directive stating that we should allow ourselves to accept abuse. “Turn the other cheek” doesn’t suggest that you allow yourself to continue to be hit.
Many people who suffered abuse themselves—psychological, emotional, physical—try to inflict similar harm on others. The only logical response is to turn away, refuse to enable them, and understand that you can’t help them.
Quit the firm, fire your client, change associates, resign from the club, diminish time with the family member. Life is too short to be miserable.