Now that we've read phase 1 of the Willoughby-Marianne subplot, I offer this Wikipedia checklist of "Narcissistic Personality Disorder".

I don't think we can call Willoughby a narcissist (yet), but I do think their romance has elements of shared narcissism... they encourage each others' grandiose and self-centered tendencies, encourage each other to look down on "lesser" people, resist/refuse empathy, lavish each other with admiration, etc.:

"Narcissistic Personality Disorder: A pervasive pattern of grandiosity (in fantasy or behavior), need for admiration, and lack of empathy, beginning by early adulthood and present in a variety of contexts, as indicated by five (or more) of the following:

Has a grandiose sense of self-importance

Is preoccupied with fantasies of unlimited success, power, brilliance, beauty or ideal love

Believes they are "special" and can only be understood by, or should associate with, people (or institutions) who are also "special" or of high status

Requires excessive admiration

Has a sense of entitlement

Is interpersonally exploitative

Lacks empathy

Is often envious of others or believes others are envious of him or her