This is life confirmation bias, to project all the blame onto the person they want to make jealous and it confirms that it's the other person who has all the problems and is always that way about everything. If this is internalized, it can manifest in many unsettling ways - and the person being made jealous will come to believe that's what they're always like and the other things the narcissist may say to them. I think a lot of self knowledge and honesty is necessary to overcome this, as it's possible that the narcissist already knew al the weakness of the other person anyway from the start, and knew how to manipulate the person. That is why self acceptance and love is especially important as a protection. As the narcissist is unlikely to genuinely love the other person, they won't care what they say or how they make them feel. The responsibility lies with the other person to stop in some way this behaviour. Trying to make the other person jealous is something they enjoy, and shows a lack of empathy towards that person, as they know the things they do and say must make them feel rotten. It's a vicious cycle, unless broken. They won't change and suddenly become faithful, loving and kind, and their own coping mechanism is control. If the person they want to "fall" for all their antics isn't up for game, there are ways to get them out of the game, rather than change themselves. The only change therefore is that they've stopped playing the games as they know they won't win, and they don't want to waste their time or feel bad. There is no other way but to accept this, rather than try to change someone is not capable of it.