The Law of Chastity
22 Thou shalt love thy wife with all thy heart, and shalt cleave unto her and none else.
23 And he that looketh upon a woman to lust after her shall deny the faith, and shall not have the Spirit; and if he repents not he shall be cast out.
24 Thou shalt not commit adultery; and he that committeth adultery, and repenteth not, shall be cast out.
President Howard W. Hunter said:
“A man who holds the priesthood shows perfect moral fidelity to his wife and gives her no reason to doubt his faithfulness. A husband is to love his wife with all his heart and cleave unto her and none else (see D&C 42:22–26). . . .
“The Lord forbids and His church condemns any and every intimate relationship outside of marriage. Infidelity on the part of a man breaks the heart of his wife and loses her confidence and the confidence of his children (see Jacob 2:35).
“Be faithful in your marriage covenants in thought, word, and deed. Pornography, flirtations, and unwholesome fantasies erode one’s character and strike at the foundation of a happy marriage. Unity and trust within a marriage are thereby destroyed. One who does not control his thoughts and thus commits adultery in his heart, if he does not repent, shall not have the Spirit, but shall deny the faith and shall fear (see D&C 42:23; D&C 63:16).”
(“Being a Righteous Husband and Father,” Ensign, Nov. 1994, 50.)