What does the Bible say about adultery?

The word adultery is etymologically related to the word adulterate, which means “to render something poorer in quality by adding another substance.” Adultery is the adulteration of marriage by the addition of a third person. Adultery is voluntary sexual activity between a married person and someone other than his or her spouse.

The Bible begins its teaching on marriage with the pattern of Adam and Eve:
one man and one woman, husband and wife, united by God (Genesis 2:24, Mark 10:7–9).

The Bible clearly condemns this act

(Exodus 20:14)You shall not commit adultery.”
It violates the commitment made in marriage to be faithful to one’s marriage partner.

Jesus puts both of these “strategies” to rest: “Anyone who divorces his wife and marries another woman commits adultery” (Luke 16:18).
And, “Anyone who divorces his wife and marries another woman commits adultery against her. And if she divorces her husband and marries another man, she commits adultery” (Mark 10:11–12).
According to Jesus, divorce does not circumvent the prohibition against adultery.

Flee sexual immorality

So, what should you do? The Bible’s instructions are clear. Guard your heart and flee from evil. When you feel that hint of attraction, it’s time to flee. Get out of the situation as soon as you can because anything less is agreement with adultery. “A prudent man foreseeth the evil, and hideth himself; but the simple pass on, and are punished.” (Proverbs 27:12).

Paul warns clearly against all such behavior: “Flee sexual immorality. Every sin that a man does is outside the body, but he who commits sexual immorality sins against his own body.” (1 Corinthians 6:18).
To be given a body by God is a great privilege and we can use it to honor Him who gave it: “Or do you not know that your body is the temple of the Holy Spirit who is in you, whom you have from God, and you are not your own? For you were bought at a price; therefore glorify God in your body and in your spirit, which are God’s.” (1 Corinthians 6:19-20).