Narcissists cannot accept the fact that another person does not want to be with them or even goes as far as rejecting the narcissist. Remember that a key trait of narcissists is an overblown, undeserved ego and inner belief that people are jealous of them. To them, it is simply not possible that their partner doesn't love them and can live happily without them. If the narcissist loses the attention and affirmations of just one individual that was previously well-controlled, they will go to extreme lengths to regain that control though manipulation.
Some methods of manipulation are direct, brash, and used to incite empathy from the victim. These individuals will not think twice about threatening suicide or even claiming to have a plan for their suicide. The purpose of this is to awaken the caretaker trait in the abused partner and keep them close.
Kristy Lee Hochenberger, "Micromanipulations: A Narcissist's Method of Control," Psychology Today, November 2, 2020