The Casual Vacancy, Gaia Bawden/Sukhvinder Jawanda, Sukhvinder's already taking more teasing and bullying than she can stand, and she knows that it'll only get worse if she makes her relationship with Gaia public.

Harry Potter, Bellatrix Black/Andromeda Black/Narcissa Black or some permutation thereof, They justify having a physical relationship by saying that it's practice for when they're married. But when they are married, they find that their husbands can't please them the way their sisters can.