@dlowan,
												Fairly briefly, if that's OK, Deb.
I only became aware of this "condition" as a result of post relationship break-up counseling.
Yes, it was 
extremely debilitating to be involved with such a person for a  very long time. You might ask, so why stay in such a situation for so long? Well, because a narcissist does not necessarily 
present themselves as such to other people.  This was a highly intelligent person, who also 
presented himself as a pretty sensitive, socially aware person. A very attractive person. 
That was the person I became involved with in the first place. Then, bit by bit, so slowly you'd hardly even notice .. the real personality emerged. 
So the problem became one of my original perceptions (I'd always considered myself a pretty good judge of character) & these conflicting  "episodes" where 
entirely different behaviour and attitudes would show their ugly face. I've often  wondered if narcissists only show these real aspects of themselves to people they know truly accept & love them? Because to anyone else (he holds a very responsible position) he appears reasonable, a "liberal" thinker, a kind & considerate person, quite charming, really ....
It is living & coping with the  conflicts of your own perception of 
who that person actually is  that does the damage. At least in my case. I think he actually cared for me a lot (as much as he was actually 
capable of  caring for someone outside of himself) but ....  caring for such a person can involve intricate juggling acts with your 
own perceptions.  And that is where the harm is done. I am so glad it is over & I can see things clearly again now. It has taken me quite a few years to fully "recover" myself. Now I am so glad that  that relationship is history. Because, at the worst times, I seriously wondered if I would actually survive it.