I was rather surprised by a recent Harlequin desire I started reading last night. Specifically that the hero and heroine have sex despite both knowing that he is in a serious relationship with a marriage-minded girlfriend.
They are not in, nor do they expect to be in, a relationship at the time, and they don't use protection despite both knowing she is not on the pill. Oh, and the girlfriend is in another room of the same (admitted large) house chatting with the hero's mother and other family members at the time.
There a lot of boundaries I might encourage Harlequin to push, but I am not sure infidelity is one of them. I would have thought that was rather central to the brand. Is this popping up in any of their other books?