You shall not commit adultery. [Matt. 5:28; Rom. 1:24; Eph. 5:3; Prov. 6:25, 26].
Observe here the expansion of the thought in the catechism which includes whoredom in all its forms, as well as unchastity [premarital relations, sexual impurity, and lustful desire under whatever name] [Lange’s Commentary, condensed].
Not only adultery is forbidden here, but also fornication and all kinds of mental and sensual uncleanness.
All impure books, songs, pictures, etc., which tend to inflame and debauch the mind, are against this law [Clarke’s Commentary].
– The Amplified Bible: page 93