I have spent the last 25 years of my life with a narcissistic husband. Being in a relationship with narcs is the most soul destroying experience. The one thing that they do is destroy your sense of self and with that goes your self esteem, confidence, etc. Don't for one minute think that you will be able to change them since they can not see that they have any problems. All and any problems in your relationship come from you in their mind. They have no empathy so getting them to read a letter or even having a discussion is a waste of time. You need to build up your self again and if you can do that you will also build up the courage to remove yourself from this emotional abuse. Take care and all the best.