http://www.gospelgazette.com/gazette/1999/oct/page19.shtml
Co-Habitation
“What does the Bible teach about co-habitation? ~ Dan Gannon”
Hence, usually “cohabitation” is distinguished from marriage. Further, those cohabiting may be a heterosexual couple, but they may instead be (1) homosexuals, (2) lesbians, (3) a plurality of communal, heterosexual participants, (4) polygamists or (5) incestuous parties.
Since the 1960s, several variations on the family unit have emerged. More unmarried couples are living together, before or instead of marrying. Some elderly couples, most often widowed, are finding it more economically practical to cohabit without marrying. Homosexual couples also live together as a family more openly today, sometimes sharing their households with the children of one partner or with adopted or foster children. Communal families, made up of groups of related or unrelated people, have long existed in isolated instances (see Communal Living). Such units began to occur in the United States during the 1960s and 1970s as an alternative life-style, but by the 1980s the number of communal families was diminishing. [Ibid.]It is clear that the cohabitation pertains to a sexual relationship, but without the sanction of legal marriage. Then, we approach Scripture with the understanding that “cohabitation” involves: (1) a distinction from lawful marriage, and (2) includes sexual activity.
The biblical ideal has always been one man for one woman for life, beginning with the Garden of Eden with the creation of Adam and Eve (Genesis 2:21-25; Matthew 19:4-6). However, God tolerated polygamy under Patriarchy and Judaism. Even then, though, polygamous marriage was distinguished from fornication – sexual intercourse outside the bounds of marriage. God, through the Bible, has always condemned the sin of fornication (1 Corinthians 5:9-10; 10:8), including the subclasses of adultery (Mark 10:19; Galatians 5:19), homosexuality (Leviticus 18:22; Deuteronomy 23:17; Romans 1:26-27; Corinthians 6:9; 1 Timothy 1:10; Jude 7) and certain forms of incest (Leviticus 20:14; Deuteronomy 27:22-23). (It seems certain, though, that marriage between siblings following creation, and at least between cousins after Noah’s universal flood, was not only permitted by God but necessary, to repopulate the earth. Marriage between half brothers and sisters, such as Abraham and Sarah, was also permitted under Patriarchy.)
Therefore, from evaluation of dictionary definitions and consideration of biblical material, “cohabitation” involves three elements: (1) living together as sexual partners, (2) without legal sanction, and (3) without religious sanction. However, an added distinction must be observed where contemporary legal and religious sanctions may be granted to sexual relationships that are nevertheless condemned by God in the Bible. For instance, what man calls “marriage,” on some occasions God calls “adultery.” “Whosoever putteth away his wife, and marrieth another, committeth adultery: and whosoever marrieth her that is put away from her husband committeth adultery” (Luke 16:18). Irrespective of what laws today may allow or what certain religious groups may approve, adulterous marriages and homosexuality continue to constitute unlawful (Divine law) cohabitation. As such, then, cohabitation as distinguished from marriage (whether upheld by civil law or our religious neighbors) is sinful.