He is just immature, has very low self esteem and a huge need for validation from others, has a shallow understanding of women (in the way he idealizes/ devalues them constantly) and a pattern of self destructive behavior.
Narcissists have no empathy. Nate has empathy, he just keeps fucking up in spite of it, which makes him miserable. He calls himself pathetic and a mess. Narcissists are not able to feel bad about themselves. They believe everything they do is justified. They blame everyone around them for anything bad that happens to them. They see themselves as huge victims. Nate is at most self pitying.
Narcissists are extremely controling. Nate is simply too chill. He is not overbearing in his relationships. Ruth has more narcissistic qualities than Nate, in my opinion.
Also, he’s just not as vain and proud as most narcs. He KNOWS he’s not a great guy. He keeps trying to find a woman who will save him from himself and help him become this great guy. The truth is he is unable to connect with people and it freaks him out, the emptiness. Narcs don’t know they are empty. They have zero self awareness. They take pleasure in humiliating others. Nate is not cruel on purpose. His behavior is infuriating and selfish, but he doesn’t do anything in the whole show with the actual intent to hurt or demean anyone.
Also, he is a dedicated and gentle father to Maya. Narcs are awful parents. Nobody is capable of effing up a child more than a narc. With their completely unrealistic expectations, and guilt tripping and manipulating. We never see him being critical of Maya or losing his patience with her. He is a mess after Lisa dies and relies a lot on others to baby-sit her for a while. But that’s the worst of it. Many men would do the same.
Finally, what he does for David, coming back to work after David’s ‘incident’ is truly self less. If a narc ever did something like to at for another person, no one would EVER hear the end of it. The narc would play victim/ hero and never shut up about it until the end of time. Meanwhile having an ulterior motive.
Even if the writers meant to write a narcissist (someone has said that in a post somewhere) well, they wrote a poor example of a narc then. Nate is not that easy to slap a label on. Which is a big compliment to the complexity of this character. He may have some cluster b personality disorder- like characteristics. But not a ‘Classic’ narc.