The Bible is very clear - sex is reserved for marriage as the ultimate physical expression of the relationship between husband and wife. A loving, stable, God-centered relationship is the ideal. The seventh commandment forbids sex outside of marriage, "You shall not commit adultery." (Exodus 20:14) Jesus was also clear that Christian behavior was about more than just obeying the letter of the law. "But I say unto you that whoever looks on a woman to lust after her has committed adultery with her already in his heart." (Matthew 5:26-27) The Lord was telling us that what happens in the heart matters just as much, and he will judge according. (Hebrews 13:4)