Well if your talking about narcisstic personality disorder, you are in a very unhealthy situation, and being in the relationship really could do you more harm if you stayed, than if you walked away and are grieving over the relationship. I don't know know what you have done to help yourself cope with the situation but of course it takes time to heal, and getting yourself involved with other relationships such as friends, or dating again, or family, it will help you get your mind off focusing on the individual.
NPD is one of the worst disorders to be around, and can mess with your selfesteem, as well as your self worth. It can mess with your mind as they gas light you and make you think you are going out of your mind. They control and manipulate you. It's not a very good place for anyone to be, and really you have to be thankful you are out of the situation and hopefully can heal and learn to be healthier and happier. It's whether you choose to get help, and deal with the reasons why you feel you need to be in a relationship like this. Why you got there in the first place, and how you can avoid staying out of another one. It's really about how much you want to invest in yourself to to live the best life you can. Dwelling on it, keeps your focus there. It is your past, and now you are in the moment. How can you be happy with out this person, and finding your purpose, and self worth. You deserve much better and deserve to be loved, but you have to make the effort to get there.