Yes, a believable poly relationship would be one thing, but "Not in the same way I love you, Stephen, of course!" or "That's okay, I know you'll always care for me! Now you boys get an apartment together" is quite another. It's quite difficult for a convincing open relationship to find a place in badfic, and I don't feel that it ever belongs in a story where the woman in question isn't a significant character as well. If she's simply window dressing, making her apparently complicit is just as offensive, in my view, as villifying or victimizing.