The Bible says in 1 Thessalonians 5:22 that we are to avoid the very appearance of evil. Living together without being married gives the appearance of evil and therefore should be avoided. It suggests that the couple involved is willing to limit their commitment to one another based on current feelings, instead of long-term commitment based on God’s design for marriage and His laws governing the duration and nature of the relationship. It also invites great temptation for sexual immorality, which includes sexual relations before marriage.
Genesis 2:22-25, Ephesians 5:21-33, Hebrews 13:4 and Romans 13:1 reveal both the spiritual and legal aspects of the marriage covenant. When a man and woman live together without committing to one another and to God in the spiritual and legal aspects of marriage, they violate the Word of God.
Marriage is a sacred covenant in the eyes of God. A man and woman should make every effort to honor God and each other by obeying the Word regarding marriage.