The 21st century is the age of living single. Today, the number of single adults in the U.S. — and many other nations around the world — is unprecedented. And the numbers don’t just say people are staying single longer before settling down. More are staying single for life. A 2014 Pew Report estimates that by the time today’s young adults reach the age of 50, about one in four of them will have never married. The ascendancy of single living has left some in a panic. U.S. News & World Report, for example, cautioned that Americans think the country’s...