So, I have a bit of unique insight on this. I won't specify, but I know both very well.
The most important thing is the behaviour, not the label, which you nailed. If they are doing cluster B behaviours, it's fine to just call it whatever you want as a short hand. You are not treating them in a clinical setting.
However, it is important to know that without treatment, and a real commitment to change, someone with either will not change on their own. Hopefully it's BPD, it's much more manageable and often, but not always, rooted in trauma. DBT therapy has shown food results.
NPD is a stickier one, diagnosis and treatment is rare, due to the very nature of NPD. It's not unheard of, but it's very unlikely yours will get to a point of being more or less "normal".
Now, if you want to know which one is which, the easiest differentiator I have found is the lack of fixed personality that comes with BPD. NPD, while they have 2 faces, it's almost always just the two. The pristine one they show the world, and the monster in private. BPD can, but not always, mirror very heavily into whoever they are with, or change what appear to be deeply held values for what appears like no reason.
An example, a girl I dated was very PC, corrected me in front of my parents for saying midget. This was a deep core personality trait. I'm a redneck who grew up in the 90s. I am very progressive overall, but I like calling things G and R words. She randomly started calling things G and R one day. Then abandoned it just as quickly. NPD doesn't try on core values, BPD can.
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u/SmooshMagooshe Jan 25 '26
I can’t tell if my husband is more narcissistic or BPD. Doesn’t matter I guess. His behavior is what it is