Narcissists devalue and then discard as a protective measure for their ego. In their minds, Borderlines don't devalue, they mirror. They see devaluation from the Narcissistic side (the desires of the other party) which serves as a catalyst for the "broken attachment" belief of the disorder.
we non are more comfortable with the relationship and no need to keep all the attention because we understand the real meaning of love as we know that the other loves us and dont need to hear it everyday because we know but in the BPD, they dont keep it in their mind like we do and have to have it repeated everyday and keep reminding them everyday of the same thing and always new thing. We nons cannot keep that up and thats what wears us out because we all do want to help them because we love them but they dont understand that real meaning of love.
Borderlines have a deficient, part time identity, they mirror others for good. Devaluing that good would mean that they devalue themselves. Instead, they seek out others *who evaluate them with projective identification as good objects,* in turn evaluating themselves as good objects and *offerings* to that projected good "self"- This comes with the distorted belief that this will give the Borderline safety in the World. The fantasy merger comes from the ideas of reference of BOTH parties. Since the fusional quality of the relationship IS a fantasy merge- it cannot stand reality testing - and therefore it falls apart.
The partner then withdraws in order to protect the carefully constructed false self and the Borderline flees in panic to alleviate their fear of splitting and paranoid/schizoid actions. In other words they take flight to safety- either in secret searching or in the immediate arms of another good object- while the partner (also in paranoid/schizoid) isolates in wounded ego and yearns for the missing objectification, wondering if and when they will ever return. Eventually the wounded partner (if left on their own without also finding a new objectification,) evolves through the required abandonment depression and comes out the other side with personal growth and development.