Adultery

Exodus 20:14 Thou shalt not commit adultery.
Matthew 5:27-28 Ye have heard that it was said by them of old time, Thou shalt not commit adultery. But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.

The Bible shows us that to be anything other than faithful, in mind AND body, is a sin. It is spoken so strongly against that 'lust' made it to that little list of Christian taboo; the Seven Deadly Sins. Our society has immersed itself in a pool of sexual energy and lust. To be famous, you almost have to drip pheromones. Societies similar to ours mentioned in the Bible that God destroys are referred to as harlots or whorish women. Look at the comparison between Jerusalem, Samaria and Sodom in Ezekiel 16. The chapter compares Jerusalem to a woman found in sin. The Lord took her (Jerusalem) and washed her of the sacrificial blood of her idols, decked her in fine clothing and perfume. He gave her jewels and a bed. All he asked was loyalty, faith and love. Instead, like Samaria and Sodom, Jerusalem's sister cities, the people took their gifts and used them to worship idols and to live in immoral sin and corruption. Jerusalem is compared to the woman who is given everything and uses it to bed other men. Proverbs 7:6-23 is a passage called "The Folly of the Simpleton" by some because it is the simple man's sin to be lured by lust. It is a base, carnal urge to take part in fornication, which is the reason God gave us marriage. To escape the sins of lust and fornication. Look at I Corinthians 7:9 where Paul tells us it is better to marry than to burn.

If this doesn't cover what you were searching for, check out these verses or ask a question!
Leviticus 20:10
Deuteronomy 22:23-24 - Think of Joseph and Mary as you read these verses; the thoughts Joseph must have had before the Angel of God appeared to tell him that Mary was still pure.
Proverbs 6:32
Matthew 19:9