Rejection sensitive dysphoria (RSD) and NPD - how do they compare/overlap ?

I’m mending from a break up.

My former had ADHD and by the way our relationship ended - i speculate NPD.

As i am working through the emotional whiplash, i’m wanting to understand RSD and NPD more.
What’s your take on the two?
How to spot the difference or can they go hand in hand?