Honoring Marital Vows with Complete Fidelity:
The proclamation explains that a husband and wife should "honor marital vows with complete fidelity." 

Pres. Ezra Taft Benson once said, "The plaguing sin of this generation is sexual immorality.  This, the Prophet Joseph said, would be the source of more temptations, more buffetings, and more difficulties for the elders of  Israel than any other"   Elder Neal A Maxwell has pointed out, "The seventh commandment (thou shalt not commit adultery) is one of the least heeded but most needed laws of God."
"A misconception in the world today is that infidelity involves solely the commission of sexual acts outside of marriage.  However, being completely faithful to one's spouse requires more than avoiding adultery.  Pres. Spencer W. Kimball taught, 'Marriage presupposes total allegiance and total fidelity.'  We marry with the understanding that we will give ourselves completely to our spouse and that any divergence is sin.  We show our faithfulness to God by loving him with all our "heart, might, mind and strength" (D&C 4:2).  We show fidelity to our spouse in the same ways.  Indeed, our spouse is the only other being besides God whom we are commanded to love with all our heart.  We are commanded to love our spouse with all our heart and cleave unto none else (D&C 42:22) (Hawkins, p59).
There are four types of infidelity.  Emotional: fantasy(detached) and romantic (attached) and Physical: Visual (detached) and sexual (attached).  Fantasy infidelity is characterized by having an emotional affair with someone who has no knowledge about what is taking place or with someone who is anonymous.  This type of infidelity involves fantasizing romantically about someone other than a spouse.  This can take place completely in one's imagination but  more and more emotional infidelity is being committed online through emails, chat rooms and social networking sites. Many justify their thoughts by claiming that their love is dead.  However, Pres. Kimball taught that when love wanes or dies, "it is often the infidelity of thought or act  which gave the lethal potion." (Hawkins p. 60).
Visual Infidelity/Pornography is perhaps the most common type of unfaithfulness.  Pres. Kimball said, "There are those married people who permit their eyes to wander and their hearts to become vagrant, who think it is not improper to flirt a little, to share their hearts, and have desire for someone other than the wife or the husband....Many acknowledge the vice of physical adultery, but still rationalize that anything short of that heinous sin may not be condemned too harshly; however, the Lord has said many times: "Ye have heard that it was said by them of old times, Thou shalt not commit adultery: But I say unto you, that whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart." (Matthew 5:27-28)
Romantic Infidelity occurs when an individual becomes emotionally involved with a specific person other than his or her spouse. Otherwise known as emotional infidelity which is defined as having emotions or thoughts about someone other than the spouse. https://www.lds.org/ensign/2009/09/fidelity-in-marriage-its-more-than-you-think?lang=eng
Sexual infidelity -  "Whoso committeth adultery with a woman lacketh understanding: he that doeth it destroyeth his own soul. (Proverbs 6:32).  This occurs when a person engages in sexual acts outside the bonds of marriage with our without emotional attachment.  A professor and marriage counselor Veon Smith said "infideltiy is a subtle process.  It does not begin with adultery; it begins with thoughts and attitudes.  Each step to adultery is short and each is easily taken; but once the process starts, it is difficult to stop."  Satan will try to convince us that we can find happiness in infidelity. However, Pres. Benson warned, "Quickly relationships will sour.  Guilt and shame set in.  We become fearful that our sins will be discovered.  We must sneak and hide, lie and cheat.  Love begins to die.  Bitterness, jealousy, anger and even hate begin to grow."
There are obvious consequences to infidelity.  The spiritual consequences are real and serious.  There are also other negative consequences.  "Infidelity produces traumatic on the spouse...Children whose parents have been unfaithful also tend to be confused and disillusioned, and at times also experience despair." (Hawkins, p62).  Objectification, overemphasizing the visual, overemphasizing sex and instant gratification and instant solutions are also some negative consequences that come from infidelity.
Some ways to avoid and prevent infideltiy in our marriages are to establish proper and clear boundaries both within and without the marriage. "Dr. Shirley Glass points out that infidelity is more about boundaries than anything else.  She uses an anology of walls and windows. In an extramarital affair, people put up walls in their own marriage and open the window to others outside the marriage.  Instead, we must know how to put up appropriate walls to protect our marriages from outside influences and open the window of love and communication within our marriage." (Hawkins, p63)   Being on constant guard as to what we allow into our personal lives and minds and what we allow into our homes is another important protection.  Being fiercely loyal to our spouse which includes, being aware of the subtly of the adversary, controlling our thoughts and putting our spouse first. "Thou shalt love thy wife with all thy heart, and shalt cleave unto her and none else" (D&C 42:22). "Pres. Kimball related, "The words none else eliminate everyone and everything.  The spouse then becomes preeminent in the life of the husband or wife, and neither social life nor occupational life nor political life nor any other interest nor person nor thing shall ever take precedence over the companion spouse.

Steps to Repairing Marriage after Infidelity:
1. Rebuild Trust
    Becoming accountable
    Establishing Boundaries
    Rebuilding the trust bank account
2. Gain Perspective -- both spouse explore aspects of marriage and where they need improvements
3. Repentance and Forgiveness
    Confession and forsaking the sin
    Finding forgiveness
4.  Overcoming Addiction -- seek necessary help in overcoming addiction
5.  Making the Choice to Stay Together
     Healing the past
     Strengthening the Present
     Enriching the Future