I think you misunderstood. My advice is to walk away. Understanding that they have a mental illness that is incurable until they seek treatment is the key to understanding that there is no hope. I have also been abused by narcissists. I have a lot of trauma in my past and I grew up into an adult that was overly giving, overly caring, overly compassionate, and overly willing to take responsibility. That’s how my personality was malformed due to trauma: not to be mean but to be nice.
I thought that I was the problem and that I needed to change. By understanding that narcissism is an incurable mental illness (unless the person is willing to get treated) we are empowered to walk away.
I understand that many people do not believe that trauma is at the root of most mental illnesses. This is simply my opinion as someone who has treated many people for many years and been trained to doctoral level in clinical psychology. I am open to being wrong.