Will I be sinning if I have sex with my girlfriend?
In the Greek language of the New Testament is the word pornos. It refers to a person who has sex outside the bonds of marriage. It is most accurately translated as "fornicator" in English, but in some translations, the word is more vaguely translated as "sexually immoral person" or even more vaguely as "immoral person." Regardless of how it is translated, its definition remains the same. Paul points out, "For this you know, that no fornicator, unclean person, nor covetous man, who is an idolater, has any inheritance in the kingdom of Christ and God" (Ephesians 5:5). In Hebrews 13:4 we read, "Marriage is honorable among all, and the bed undefiled; but fornicators and adulterers God will judge." But probably the plainest teaching is found in Revelation 21:8. Here a list is given of those who will end up in hell. "But the cowardly, unbelieving, abominable, murderers, sexually immoral, sorcerers, idolaters, and all liars shall have their part in the lake which burns with fire and brimstone, which is the second death."
Sex within marriage is honorable, pure, and expected; but sex outside of marriage is a sin. It will cause the participants to face the wrath of God.
Often, when I explain this to young people who come to see me, their initial reaction is often, "Well, I don't believe the Bible is true anyway." In other words, they are willing to consider what God says so long as it doesn't interfere with what they have already decided to do. Yet, God's laws are not arbitrarily given. There are reasons behind the laws which benefits the person willing to follow those laws. God is not being unjust or cruel by saying you need to wait until marriage to have sex. He has good, practical reasons behind His command.
A while ago I wrote two articles on this matter and I would appreciate it if you would take the time to read both of them. The first is "Why Sex Outside of Marriage is Wrong" and the second is "Waiting for the Proper Time." Let me know what you think of the information presented. I would like an opportunity to address any comments or concerns you may have.