I am not referring to two college mates sharing an apartment or something like that, but rather two unmarried people of the opposite sex living together in an intimate relationship. Premarital cohabitation seems to be the accepted norm today and many, even professed Christians, engage in it thinking that it is an innocent lifestyle that God winks at. Two people living together and making babies with the intention of getting married is outright disobedience to God's command. It probably has a higher risk for divorce too. I know some hold that living together before marriage is fine as long as there is no sexual intimacy however it follows fornication, it could be a stumbling block to the other individual, and a wise person will avoid such situation that can lead to temptation to sin.Cohabitation is NOT fornication. Cohabitation is living together/ shared housing. Fornication is having illicit/sinful sex. The two words are entirely separate and distinct terms. "Shacking-up" means cohabitating as if married without the benefit of the MARRIAGE... sometimes referred to as a "try-out marriage"... it is sinful.
Gen 2:24- Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh. You become one flesh through marriage which God will recognize, not cohabitation.