You have to keep in mind that there's a difference between someone with narcissistic tendencies than someone with Narcissistic Personality Disorder. Everyone has narcissistic tendencies, some more than others and NPD is apparently rare but who knows as they are perfect so...
Narcissism seems to be a buzz topic, it is literally everywhere and I think people are confusing selfish, manipulative people with narcissists as a lot as it kind of crosses over.
In my case, I suspect I was with a covert narcissist as in full NPD because their history, behavior and the abuse fits the Narcissistic Abuse Cycle perfectly, as does my health as a result. Even then I cannot say for sure as they are not diagnosed, however third parties are noticing it, they are losing control of themselves at the moment.
All I will say is, and there may be others who have maybe experienced what I have, that it is beyond that of a normal person. It is living with someone who is quite literally insane, they are not well.
Highly emotionally and psychologically abusive and very manipulative with rage that goes into physical. They are not ticking on the same level, nor do they interpret the world the same or see people as individuals. They are batshit crazy, they are intelligent but at the same time they are delusional.
It is Jekyll and Hyde, one is nice and highly intelligent able to fool everyone and the other is sick and twisted, insane and unintelligent. That's what I have found anyway.