NY Times – By MEG JAY – Published: April 14, 2012 – Cohabitation in the United States has increased by more than 1,500 percent in the past half century. In 1960, about 450,000 unmarried couples lived together. Now the number is more than 7.5 million. The majority of young adults in their 20s will live with a romantic partner at least once, and more than half of all marriages will be preceded by cohabitation. This shift has been attributed to the sexual revolution and the availability of birth control, and in our current economy, sharing the bills makes cohabiting appealing. But when you talk to people in their 20s, you also hear about something else: cohabitation as prophylaxis.