Dr. David B Hawkins discusses some of the dangers when one gets involved in a relationship with a Narcissist, especially to one’s Self Esteem.
The video also has some sound advice regarding Boundaries.
Video is courtesy of the David Hawkins YouTube channel
The one point that he makes that I disagree with, is about being able to change a Narcissist. It is my opinion, and your mileage may differ, that Narcissism is a Hard Wiring problem caused by major Attachment Trauma(s) suffered when the Narc was a tiny infant. There is no Treatment Protocol for Narcissism, and many Licensed Therapists will agree.
Trauma caused later in life, also changes Brain Chemistry and it is very hard to treat, just ask anyone with PTSD or Complex PTSD, but can be treated.
I also think that it also depends on the depth on the Narcissistic Disorder. A Malignant Narcissist IMHO cannot be changed and it could be dangerous to even try to get them to change. Someone who is not deeply disordered, just maybe could adapt to you setting boundaries etc.