Liz, after being in a relationship with a NPD narcissist, the only advice that was given to me that worked was, "View him with pity. From a great distance."
My exNPD is remarried now and I feel very sorry for his new wife. He hooked her after a very short courtship and I know she is deeply unhappy and he doesn't give two whits about her. I feel worse for the kids, my DS13 included. They spend a lifetime trying to please a father who doesn't see them, doesn't care about their needs, and being disappointed over and over and over again by his empty promises and his arrogance and entitlement. It's death by a thousand cuts.
I'm not surprised by the diagnosis from all your stories. I hope you realize what this means. For this marriage to "work," you need to be willing to subsume yourself completely to his desires for the rest of your time together. NPD is not touched by therapy and medication. It's a personality disorder -- this is WHO HE IS, forever, and to everyone.