I don't think it was totally unbelievable: two couple of males frequent a gay/bi bar, where there's a gorgeous girl both couples want to add as their third. She (logically) thinks they're gay, but they're all bi. So they all have this weekend romp. She overhears a part of a conversation (not even a bad part, I don't think) and she FLIPS out and leaves. That was the part that just didn't make sense to me, but that scenario is in so many books. Someone misinterprets something and just leaves without giving anyone a chance at a rational explanation. And it's not like they were even treating her the way she interpreted the conversation. So while I enjoyed the story, that part sort of ruined it for me. I don't think I'll read the follow-up.