Living together does not constitute a marriage. The Lord met the woman of Samaria. She had lived with five husbands and the Lord called them husbands. But how about the man she was currently living with? The Lord refused to give him the status of a husband. He said, “And he whom thou now has is not thy husband.” (John 4:17,18) The differentiation is very clearly given. Marriage is never a private affair. Two people are not married when in private they commit themselves to each other but when they do so in the presence of witnesses before God. Our Lord and His mother attended the marriage feast at Cana of Galilee. Obviously, there was an event which was given public and official recognition, and all acquaintances then knew that the two people were duly married.
Homemade, Dr. Spiros Zodhaites
Pretty simple to me: A marriage before God creates a supernatural ‘one flesh’ relationship, recognized and upheld by God Himself. Living together, does not. Clearly then, if you are living together, unmarried, you must either marry, or move out, to get right with God.