Sex before or without marriage is discussed in the Bible as a form of adultery. Therefore, it is a sin to have sex without marriage. Of course this rule doesn’t include those who have been raped and sexually abused.
Adultery is conjugal infidelity. An adulterer was a man who had illicit intercourse with a married or a betrothed woman, and such a woman was an adulteress. Intercourse between a married man and an unmarried woman was fornication. Adultery was regarded as a great social wrong, as well as a great sin.
The Mosaic law (Num. 5:11-31) prescribed that the suspected wife should be tried by the ordeal of the “water of jealousy.” There is, however, no recorded instance of the application of this law. In subsequent times the Rabbis made various regulations with the view of discovering the guilty party, and of bringing about a divorce. It has been inferred from John 8:1-11 that this sin became very common during the age preceding the destruction of Jerusalem.
Jesus gave us the clearest spiritual as well as physical application of God’s Commandment to not commit adultery. “But I say to you that whoever looks at a woman to lust for her has already committed adultery with her in his heart.” (Matthew 5:28, NKJV throughout)
God promises blessings to His people when they obey Him and do not sin. When we do not commit adultery, we are also protected from other things in this world such as, sexual diseases, unhappy relationships, divorce and unwanted pregnancy. “For all that is in the world — the lust of the flesh, the lust of the eyes, and the pride of life — is not of the Father but is of the world. And the world is passing away, and the lust of it; but he who does the will of God abides forever.” (1John 2:16-17)
Is living together without marriage a sin?
Living together is for married life, not before. It would be extremely exceptional to live together and not ending up having sex. There are several Scriptures on this subject, like: “Flee sexual immorality. Every sin that a man does is outside the body, but he who commits sexual immorality sins against his own body.” (1Corinthians 6:18, NKJV throughout)
The point here is to avoid the opportunity, or, as the Bible says, flee it. Proverbs 6:24-35 deals with the sex sin as a whole, but verses 27-28 pinpoints the problem that the two people will face by living together and not make love: “Can a man take fire to his bosom, and his clothes not be burned? Can one walk on hot coals, and his feet not be seared” (Proverbs 6:27-28)
God’s wisdom says this is not allowed because we can not do it. If we are honest to ourselves we will recognize this fact. Some people think that having sex means only the actual intercourse, but really a couple does not need to go “all the way” to have sex and commit sin. There are other sexual acts, besides intercourse, that belong to marriage life, and others that should never be done.
We can claim many promises from the Bible for living righteously. There are tangible benefits and blessings in this life for obedience to God’s laws: “Observe and obey all these words which I command you, that it may go well with you and your children after you forever, when you do what is good and right in the sight of the Lord your God.” (Deuteronomy 12:28)
Abstaining from sex before marriage is an investment in the future. It will bring a much happier and successful marriage. It is God who promises it. Although it entails a little sacrifice, it goes a long way to produce character in the couple, an element so important in marriage. It certainly promotes faithfulness, a rare virtue today.
We are here in this world for the purpose of overcoming and developing a strong spiritual and godly character within ourselves. God promises those that overcome will be called His sons and daughters and will live forever with Him. Although it is a given fact that it is very hard to live godly in this present society, but as sons and daughters of God, it is our task to strive to be perfect as our Father who called us and accepted us is perfect.
The best way to resist temptation is to fight it by faith trough prayers and meditations. We have to control ourselves and discipline it so that we can not afford to sin. Apostle Paul learned to discipline his body and bring it to subjection to keep away from sinning. 1Co 9:27 But I keep under my body, and bring it into subjection: lest that by any means, when I have preached to others, I myself should be a castaway.