The dictionary defines “adultery” as “voluntary sexual intercourse between a married person and a person who is not his or her spouse.” The Bible would concur with this definition.
In Leviticus , God told Moses, “Do not have sexual relations with your neighbor's wife and defile yourself with her,” and in Deuteronomy , we find a similar definition: “If a man is found sleeping with another man's wife, both the man who slept with her and the woman must die.” It is clear from these definitions that adultery refers to a consensual sexual union.
Adultery is the complete corruption of God’s good creation of marriage.
Through the sin of adultery, Satan tempts us to seek sexual fulfillment in avenues other than the one God has ordained—within the bounds of monogamous, heterosexual marriage.
Be that as it may, it is safe to say that if a person who is married willingly seeks a sexual encounter with another person, whether or not that person is also married, both people are guilty of committing adultery.
God’s reasons for instituting His commandment against adultery are two-fold.
The negative part of the command is self-explanatory: Do not commit adultery.
Regarding sexual sin, the Apostle Paul said, “Flee from sexual immorality.Every other sin a person commits is outside the body, but the sexually immoral person sins against his own body” (1 Corinthians ).When it comes to sexual sin, the best course of action is to remove ourselves from temptation and avoid such situations altogether.Adultery rips at the fabric of society because it tears apart marriages and families which are the building blocks of society.God’s law in general, and the 7th commandment in particular, is held up as the standard for Christian behavior.
One can make the argument that wrapped up in this prohibition are all sorts of sexual sin (e.g., incest, fornication, homosexuality, etc.), and that argument can be made on the basis of chapters such as Leviticus 18.