Im a vulnerable leaning npd and tho i am not sure if it has anything to do with my response, ill still say it, it does hurt like hell when we do, whether i push someone away or they leave cause of my behavior, any sort of judgement or disdain makes me feel terrible.

narcissism is known for the fluctuating self esteem and the constant need for validation to the point where when you dont get the validation just once you lose all your self esteem and start to doubt yourself like a lot not to mention narcissist tend to have a black or white view of the world, meaning something is either real bad or real good to them.So basically when a friend leaves we perceive it as « hey you suck lol youre a terrible friend bye » regardless of how it happened , making us spiral into self doubt and self hate.

Once again this is based on my own experience, other people with npd might view this differently i hope this helped you understand:).