"We have fun and we enjoy each other's company, so why shouldn't we just move in together?"--Lauren, from Cohabitation Nation Living together is a typical romantic rite of passage in the United States today. In fact, census data shows a 37 percent increase in couples who choose to commit to and live with one another, forgoing marriage. And yet we know very little about this new "normal" in romantic life. When do people decide to move...