The answer is….
If your boyfriend merely has narcissitic tendencies…and we all do, then there is a chance.
If your boyfriend has fully blown NPD, then you need to understand: He does not love you and he never will. He hates you and will destroy you if he has the chance,
As a "codependent" person, it is your way to try to "help" people. IF you act on that impulse with a true narcissist then your mental and physical health will be eroded until you are a wreck.
I'm sorry, but there is no cure, or even anything like an effective treatment for malignant narcissism available now. The state of the art is just not good enough.
IF your boyfriend is really an NPD person (actually only 1.0 % of the population fits that description–it is a fairly rare disorder) then you have to choose: do you want to live and grow and enjoy your life, OR do you want to become mentally ill, and perhaps die.
You can't diagnose psychiatric disorders without a psychiatrist. You CAN diagnose abuse, however.
IF you find that you are in an abusive realtionship then there is one way and only one way that you can remain in a realtionship with that person and come out of it whole and healthy. That is if your boyfriend says "I realize I have been abusing you, that I am an abusive person, and I am committed to doing the work I have to do to change myself into a person worthy of being with you or with anyone."
If that is not his position, then I recomend that you run for your life.