leaving aside the fact that the only ones who would see the hypothetical betrayal are the players who are interested in Quinn and who are no longer interested in Jill.
that MC can have sex or at least be interested in Bianca I take for granted, otherwise DPC wouldn't have introduced us to her, but the premise of betrayal remains basically useless. unless you want to suggest that Jill's friends are swingers (I don't think so), it would still be a very low blow to have sex with your best friend's boyfriend, just because she's grieving over a betrayal, indeed from a girl relationship point of view it would be even worse (since I've suffered so much, I want you, my best friend, to suffer like me..)
as with Zoey, to make Bianca a believable temptation there will be a lot of work to do, of course the betrayal could be a premise, but of a longer development
anyway the scene is absolutely hilarious, Quinn despises Jill and her way of life where appearance counts much if not more than substance, and involuntarily denigrates two people who belong to that very circle, caught in a "disreputable" if formally romantic moment. but beyond that I see little