Right from the very beginning of the Bible, it is evident that God wants sex to be within marriage. For when Adam and Eve are in the Garden of Eden it is once the two have become united (in marriage) that they become one in flesh – NOT BEFORE.
Genesis 2: 24 For this reason a man will leave his father and mother and be united to his wife, and they will become one flesh.
Following this there are examples all throughout the Bible of avoiding sexual immorality, that is, sex outside of a marriage. God sees sex as so valuable that it has to be kept for the right person.
For Christians, your boyfriend/girlfriend is someone else’s future husband/wife – God wants us to respect that: 2 Timothy 2:22 says Flee the evil desires of youth, and pursue righteousness, faith, love and peace along with those who call on the Lord out of a pure heart.
Here is evidence from the bible that God wants us to avoid sexual immorality, that is, sex outside of marriage:
Galatians 5:19-25 19The acts of the sinful nature are obvious: sexual immorality, impurity and debauchery; 20idolatry and witchcraft; hatred, discord, jealousy, fits of rage, selfish ambition, dissensions, factions 21and envy; drunkenness, orgies, and the like. I warn you, as I did before, that those who live like this will not inherit the kingdom of God. 22But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, 23gentleness and self-control. Against such things there is no law. 24Those who belong to Christ Jesus have crucified the sinful nature with its passions and desires. 25Since we live by the Spirit, let us keep in step with the Spirit.
1 Corinthians 6: 9-11 9Do you not know that the wicked will not inherit the kingdom of God? Do not be deceived: Neither the sexually immoral nor idolaters nor adulterers nor male prostitutes nor homosexual offenders 10nor thieves nor the greedy nor drunkards nor slanderers nor swindlers will inherit the kingdom of God. 11And that is what some of you were. But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God.
And then 18-20
18Flee from sexual immorality. All other sins a man commits are outside his body, but he who sins sexually sins against his own body. 19Do you not know that your body is a temple of the Holy Spirit, who is in you, whom you have received from God? You are not your own; 20you were bought at a price. Therefore honour God with your body.
1 Thessalonians 4
Living to Please God
1Finally, brothers, we instructed you how to live in order to please God, as in fact you are living. Now we ask you and urge you in the Lord Jesus to do this more and more. 2For you know what instructions we gave you by the authority of the Lord Jesus.
3It is God's will that you should be sanctified: that you should avoid sexual immorality; 4that each of you should learn to control his own body in a way that is holy and honorable, 5not in passionate lust like the heathen, who do not know God; 6and that in this matter no one should wrong his brother or take advantage of him. The Lord will punish men for all such sins, as we have already told you and warned you. 7For God did not call us to be impure, but to live a holy life. 8Therefore, he who rejects this instruction does not reject man but God, who gives you his Holy Spirit.