“She knew the deal when she signed up.”
You know how sometimes people in multipartner relationships say “Well, this person agreed to that kind of relationship dynamic when they signed on, so they have no room to bitch” when it comes to disposing of partners that have become inconvenient or distracting?
That doesn’t work in reverse, where the third person tells the cranky person “Look, you people agreed to have a relationship with me, and that’s what you signed up for, so you’ve got no room to bitch about it now. Fix your shit and get your head back into the game.”*
It doesn’t work because it’s asshole logic.
It’s asshole logic no matter who uses it.
Today, I vote it off the island.
* Same thing goes for “This person needs to respect the relationship.” Tit-for-tat, man. Either respect all the relationships, or not, but cherrypicking which relationships are worth respecting and which relationships are disposable is a shitbird move.