"If the family trends of recent decades are extended into the future, the result will not only be a growing uncertainty within marriage, but the gradual elimination of marriage in favor of casual liaisons, oriented to adult expressiveness and self-fulfillment. The problem with this scenario is that children will be harmed, adults probably no happier, and the social order could collapse." (David Popenoe in Promises to Keep)
Cohabitation by definition is two unmarried people of the opposite-sex living together. It has been called by various terms, such as "living together", "shacking up", "c…