My Husband's Girlfriend : A Novel

Neil and Anya Meadows are stuck in a sexless marriage. Anya suffers from a hormonal disorder that leaves her with no sex drive at all, while Neil has a voracious sexual appetite. After an unfulfilling encounter too many, they make a deal: Neil will be allowed to have a mistress, but only for oral sex and only twice a month--and he's forbidden to fall in love with her. However, things don't exactly work out as planned.--From publisher's description.