If you do, you will be sending a bad message to the unbelieving world, and you will be putting yourself and your girlfriend into temptation in a major way. Although much of the unbelieving world does not have a problem with couples living together outside of marriage, the Bible has much to say about this type of situation. God calls us to live in the world but not live like the world. Living together before marriage is commonly accepted these days but that does not mean Christians need to partake in liberal promiscuous lifestyles.
Even if you were not going to partake in a sexual relationship together, others most likely would perceive that you are, and it would be damaging to your testimony and might also cause others to stumble. Living together outside of marriage might cause some people to think that it is okay for Christians to live together without a marriage covenant but sex before marriage, fornication, is a sin and must be avoided.
“Therefore let us not judge one another anymore, but rather resolve this, not to put a stumbling block or a cause to fall in our brother’s way” (1 Thessalonians 14:13).
“But when you thus sin against the brethren, and wound their weak conscience, you sin against Christ” (1 Corinthians 8:12).
“Flee from sexual immorality. All other sins a person commits are outside the body, but whoever sins sexually, sins against their own body” (1 Corinthians 6:18).
Marriage was instituted and designed by God. His design for relationships is at the heart of marriage, which involves companionship and intimacy, a full commitment blessed by the Lord. We must be respectful of His teachings and realize that what He commands is best for us.
“And the LORD God said, “It is not good that man should be alone; I will make him a helper comparable to him.” Therefore a man shall leave his father and mother and be joined to his wife, and they shall become one flesh” (Genesis 2:18, 24).
“Marriage is honorable among all, and the bed undefiled; but fornicators and adulterers God will judge” (Hebrews 13:4).
It is best to wait and live together only under the sanctity of a marriage covenant blessed by God. Be respectful of Him and honor your partner by being true to God’s Word. The way we live our lives is a reflection of our true character and the depth of our devotion to the Lord and His principles.
“It is God’s will that you should be sanctified: that you should avoid sexual immorality; that each of you should learn to control your own body in a way that is holy and honorable, not in passionate lust like the pagans, who do not know God; and that in this matter no one should wrong or take advantage of a brother or sister. The Lord will punish all those who commit such sins, as we told you and warned you before” (1 Thessalonians 4:3-6, NIV).