In the backstory to Bad Company and the rest of the Dictel trilogy, Drusilla Becket doesn't let her estranged ex-husband Cedric Thomas to have their two daughters over or even visit them much. However, whenever Charlie and Desiree are allowed to live with their father, they act as if they have just been liberated from a fascist dictatorship. The Richter-Thomases (at least starting with Cedric's generation) have a loose and liberal attitude toward nudity, for instance; and so the first thing the girls do is throw off their clothes and run around like "wild savages", or wild animals newly liberated from their cage. After Desiree seduces Charlie for the first time, the sisters are ardently affectionate around everybody else, and use as much of their private time as they can for making love.
Their father allows this. His own sisters won't have it otherwise.
Actually, in fact, their father — and both their stepmothers (Cedric's first wife Betty Shears and third and current wife Hope Reston [Shira's mother]) — fully accept their decision to commit themselves to each other as lovers. Their aunts (Cedric's sisters) Willa and Reva actually encourage them, since they themselves are longtime lovers themselves, as it turns out. (In fact, in Black Science, when Dr. Julian Blair treacherously leaves Willa for Dictel Corporation, the first person Willa will turn to is Reva.)
This becomes one huge reason for Drusilla to continue trying to keep Charlie and Desiree away from Cedric as much as possible. Dru tries to stop her daughters from doing what Dru considers repulsive. However, when she finds that her punishments only succeed in reinforcing their desire with defiance (they're teenagers, after all, and teenagers rebel), she is stuck with the hard choice between allowing the affair to go on and threaten both Charlie's career and the Becket family reputation, and forcing Charlie and Desiree apart using thos bluntest of all blunt instruments: Dictel and the law.
I'll need to plant this backstory in places throughout the story, not limited to flashbacks. Maybe I should gradually reveal it. The relationship line climax needs to have a strong foundation not only in the actions Charlie and Desiree take within the story, but in their shared past beyond the story as well.