A process of devaluation is in full operation throughout the life of the relationship. This is the ungrateful, FULL TIME, draining job of being the Narcissist's significant others. But humans are not instruments. To regard them as such is to devalue them, to reduce them, to restrict them, to prevent them from realizing their potential. Inevitably, Narcissists lose interest in their instruments, these truncated versions of full-fledged humans, once they cease to serve them in their pursuit of glory and fame.
Narcissists are addicts.
They are no different to drug addicts. Narcissists home on potential supplies like cruise missiles with the most poisonous load. They are excellent at imitating emotions, exhibiting the right timely behaviors and at manipulating. All generalizations are false, of course, and there are bound to be some happy relationships with Narcissists. Narcissists can be happily married to submissive, subservient, self-deprecating, echoing, mirroring and indiscriminately supportive spouses.