In this case though, they're saying their partner is pansexual - open to many kinds of sexual activities. And they're saying that they'd be accepting if their partner needed to go and do sexy stuff with someone else even though it'd cause them a lot of pain (that's my reading of it, not having a platonic friendship with someone else as you mentioned). I'm asking why? Having a different to hetrosexual appetite before going into a relationship shouldn't give you special rules once you're in one - it's absolutely no different than if a hetrosexual person wanted to sleep around. OK if your relationship allows for that, really not OK if it's going to cause your partner/spouse/love pain, as they said.
FWIW my wife is bi and dates women, not that really ever bothered me but in no way has it ever been more damaging to our marriage beyond basic scheduling conflicts. I will admit I would have had a much harder time opening up to her being with other men though. Im lucky that she has never fallen in love and wanted to run away with one of em I guess, but partly thats because our marriage is otherwise great and shes already free to explore her gay side so why would she want to leave?
https://www.amazon.com/Designer-Relationships-Monogamy-Polya...
If you had come into the relationship with the understanding that you'd both date/have sex with other people then great; it doesn't matter what other people think. However, when you say that it was hard for you to accept her being with other men, and that you're lucky that "she has never fallen in love and wanted to run away with one of em", damn. My first instinct is that you should take your own advice: find or design a relationship where you don't have to accept this.
I realize that some of my knee jerk reaction might just be instinct/cultural values, I mean no disrespect.
It's not up to debate whether or not I accept cheating because I've already set it as an immovable barrier multiple times: come into sexual contact with anybody else during the marriage and she's going to be thrown out of the window with all of her belongings.
But if she comes to me with honesty and hasn't done anything yet - why would I want to be on bad terms with her as she leaves? I can only be sad at her decision.