Well, I can't imagine how you might benefit from a "diagnosis" of NPD, except in a Family Law battle. If that's the case and you wish to have some ammunition to use in Court, insist upon discussing NPD with your counselor. If your counselor won't allow you to discuss your concerns, your obvious abuse (THAT should be enough ammo for Court), and the issues that are surrounding your relationship with him, find another counselor that specializes in domestic violence, abuse, and NPD survival. Remember, YOU are paying your counselor's salary and they should be willing to at least help you to define what you've tolerated so that you can move on. Again, I urge you to be completely honest and forthcoming in your sessions and don't minimize the events that have occurred during your relationship with him.
Another important thing to note is that there will be no closure with an NPD - Survivors have to walk away with whatever they have left intact.