As I was doing some work on the Rutherford Co., NC Marriages from 1865+ foward I ran into some marriages in which the documents said they had been living together for some time and was getting married. One pair in particular had been living together for about twenty-five years and had several children. Most of these are in my Photos of Marriage Licenses for Rutherford County, NC. I don't remember the names so I can't go directly to them but there were several. Knowing this, I would assume there were probably plenty of them that lived together most of their life and was never married. I would also assume that the farther back in time the more prevalent it was. Maybe this helps a little. Bill