Narcissistic relationships are quite addictive for both individuals. But that addiction looks different for each of them.
The victim of narcissistic abuse is addicted to the peaceful moments and love bombing. Love bombing is when they become whatever it is that you desire in the relationship. Your "perfect match." When these moments come, it is such a huge relief from the blaming, guilting, gaslighting, circular conversations and victim mentality. These moments of relief give the victim a massive hit of dopamine and erase months of bad behavior. Overtime, no matter how small the breadcrumbs get, the target of narcissistic abuse is addicted to them.
The narcissistic individual is addicted to all the effort their target pours in to pull them out of their abusive behavior. They are experts at playing the victim. Whatever you did that hurt them gives them a free pass to now treat you however they choose. Since their bad behavior is all your fault, you now pour massive amounts of time, energy and effort into making them feel better about themselves and about you. They are addicted to those intense efforts. Thus the bad behavior must continue in order for them to get their "fix."