As a young man in the LDS church too much emphasis was placed on maintaining sexual purity and not enough on gaining the light of God. When you are full of the spirit of God you abhor sin. You shudder at the thought of betraying God. On the other hand, when you place your heart on the world, temptation more easily besets you. I do not think it’s possible to entirely remove temptation in your life, but the more you seek and gather God’s light the more easily you avoid evil’s darts. You should not spend your time trying not to lust, you should spend it drawing closer to Christ.
This is not to minimize how hurtful sexual sin can be, especially in marriage or amongst families, or sexual abuse which can leave horrific wounds for generations. Suffice it to say that God is quick to forgive. One of the justifications LDS teachers used emphasizing the seriousness of sexual sin is Alma’s council to his son Corianton, where seemingly a young man’s indiscretion is placed on par with murder. This is simply not the case in the eternal scheme. A more careful reading shows that the truly grievous sin is forsaking the light and knowledge of God, this is the dreadful sin on par with murder for many reasons, one of which is it leads you into every temptation and sin. Not to mention the literal damnation upon you.
Following Alma’s brief rebuke, he launches into teaching his son further light and truth regarding the plan of happiness, revealing mysteries of the afterlife, teaching doctrine, and does not spend any more time than necessary divesting a list of do’s or don’ts of sexual matters or any other sin. He knows the light of God will have a more powerful effect changing the heart of his son than making him feel guilty about an indiscretion.
With this new emphasis in mind, I recommend reading Alma’s words to Corianton in RE Alma 19:1. Note that Alma’s hurt is centered on his son leaving the ministry, he repeats this twice bracketing the sentence on the harlot Isabel, and the rest of the verse is explaining how grievous it is to sin against the light you’ve been given, admonishing those who “murdereth against the light and knowledge of God.”
I have rewritten this verse in my own words:
My son Corianton, I have been disappointed in your conduct and need to spend more time teaching you than I have your brothers. You have seen their faithfulness and diligence in keeping the commandments of God, and they have set a good example for you. You ignored my council as we were among the Zoramites and went around boasting of yourself and your strengths. You also broke my heart when you left the ministry and went to the land of Siron among the borders of the Lamanites after the harlot Isabel. Her reputation has stolen the hearts of many, but this was no excuse for you, my son, and you broke trust with me and with God when you left the ministry and rejected your calling from God to preach to the people. Do you not realize how grievous this sin is? Forsaking the light and knowledge of God is one of the most serious sins, and the only sins worse are removing the holy ghost when it once had a place in you or murdering innocent people. If you receive the holy ghost, or the truth of all things and record of the Father and the Son, then subsequently reject it, this is a sin which is unpardonable. Murdering innocent blood causes considerable repentance, and it is not easy to obtain forgiveness, just as it is not easy to obtain forgiveness if you murder the light and knowledge of God within you.