If you confront a narcissist with their shortcomings more than likely it will be flipped around on you. They may react with rage, circular arguments, and proceed to tear you apart. They may even react with violence. They protect the false self at all cost due to their defense mechanisms. The false self is all the narcissist has left it is life or death to the narcissist protecting and preserving the false self. If you confront the narcissist with a shortcoming you injure them. This will ignite their fury (defense mechanism) which sends them into action to recover from the wound. In order to recover they need fuel. Every emotional reaction you give them during an argument or disagreement is fuel to the narcissist. You will be punished for confronting the narcissist with a shortcoming.
The only time I have seen a narcissist pretend to want to make a change is when they are in danger of losing their spouse (supply source). If you stay or go back to the narcissist thinking they are going to change this is a big mistake. Change never happens. You will be punished for thinking about leaving them, or if you did leave them and go back, you will be punished for leaving. It creates a great narcissistic injury if you leave them first. They call all the shots they say when it’s over. The narcissist needs to control those around him because his fake illusionary world and his fragmented false self is a construct and only exist if others believe the illusion as well.
If they come back around pretending like nothing ever happened it’s because they have recovered from the wound, or they come back to punish you for wounding them. The narcissist ego is fragile. They are slighted very easily.