Heh, yep. I don't think I could ever actually write NTR. The idea of a pathetic protagonist just doesn't have any appeal to me. And as a person who's been in poly relationships it's difficult for me to put myself in the headspace of someone who feels that way. I guess I just lack those exclusivity instincts so writing a character that has them will be a challenge.
I am planning for one of my characters to have a partially exclusive relationship with the main character, where she only has sex with him but is fine with him still having sex with whoever he likes.