A narcissist’s fixation is driven entirely by their need for "narcissistic supply" (attention, control, validation, or emotional reactions). They will generally continue their behavior until that supply completely dries up or until they secure a new, more satisfying object of obsession
Narcissists rarely leave a gap between their targets. If they already have a "backup" person lined up, they may drop their current target instantly. If they have a hard time finding a new source of attention, they may drag out the harassment of their former target for years.
Narcissists thrive on emotional responses—both positive and negative. If a target responds with anger, fear, or attempts to reason with them, it rewards the narcissist with a sense of control, lengthening the obsession.
If the target was the one to end the relationship or went "No Contact," the narcissist experiences a severe blow to their fragile ego. This rejection often triggers "narcissistic rage," causing them to double down on harassment (through stalking, smear campaigns, or constant messaging) to reclaim a sense of superiority