Pulling on his pants after our intimate encounter in my Las Vegas hotel room, the cute 23-year-old I’d just picked up holds out his cellphone, urging me to tap in my number. “You really don’t have to take it,” I say. Having sex with a stranger is thrilling, but I’m not that interested in a repeat performance. Two minutes after he’s gone, I climb back into bed and text my husband, Scott, whom I’ve been with for 18 years. “Just saying good night,” I type. “Good night, dove,” writes back Scott from wherever he is. Scenarios like these were typical...