Has a friend ever dumped you? What was the reason?

One word springs to mind..........Swingers!
Whatever their motives, they appear to be using people, drawing them in and the dropping them.
Not a nice way to treat genuine people and the OP is clearly better off without them. Have to wonder how many times they've done this though and what perverted pleasure they get out of it.

How sad for them they need to create drama and stress for others just to make themselves feel happy.

DH and I were once invited out to dinner by someone I worked with. It was an intimate setting with candles and a piano and couches where you drank your after dinner coffee.

They made a point of separating us, me and the man by the bar, colleague and DH sat on a couch and both employed their best flirting techniques.

We couldn’t get away fast enough.

Afterwards I learned it was some they did to spice up their relationship. They had other fantasies they acted out too, like him hitting on her in public places where they hoped a gallant rescuer would come to her aid.

Fantasies I don’t mind. It was the involving other people that was truly vile.

Weirdos