I have been meeting with a woman whose husband recently admitted he had been involved in an adulterous relationship. She was of course devastated by his admission and was seeking help to deal with her anger, hurt, and betrayal.
There is really no easy way to address these issues, because adultery rips the guts out of the marriage. The above responses are typical for the spouse who has been sinned against by adultery.
The progression of events begins with the revelation of the adultery through admission or by being caught. Once the sin is brought to light the spouse who has been sinned against typically looks for the details of the "affair." It is difficult to understand why it is so important to know these details, but for many spouses it is of great importance. However, each new revelation only increases the hurt and pain, and as the pain level increases so does the anger and realization of horrendous betrayal.
The anger is directed in a variety of directions beyond the cheating spouse and the other person. Often, the spouse blames themselves for not being "better" or more alert to subtle changes in their husband or wife. Sometimes they blame God, wondering why He would allow such a thing to happen to them. If friends were aware that things didn't seem quite right they can also be the recipient of anger by the offended spouse.
Anytime adultery takes place the marriage covenant is broken. Biblically, this can free the offended spouse to divorce their cheating husband or wife (Matt. 19:8) if they so choose to do so. Moses permitted divorce because of the hardness of the heart of the one who was betrayed but it was not always that way! However, for the Christian there is a higher principle that must be considered- the principle of forgiveness.
Not surprisingly, Forgiveness is not the road most oft' traveled. It is the biblical road for the Christian to take, and while it can be incredibly difficult, is the one that brings glory to God. You must remember that adultery is a sin like any other sin. It is not unforgivable and if the adulterer repents and both parties are willing to work on the marriage it can be repaired and be even stronger than it was previously. Forgiveness is a critical component in this process.
Without forgiveness, bitterness will quickly set into the heart of the betrayed spouse. This will lead to complicating sin issues as bitterness defiles many (Hebrews 12:15) other areas of life. Bitterness is an incredible poison that can be completely avoided if only the one who is hurt will extend forgiveness to the spouse who betrayed them.
With forgiveness, healing can and does take place in the heart of the betrayed and in the marriage itself. God is greatly glorified and grace and mercy are put on triumphant display for all the world to see! The one offering forgiveness is imitating Christ, by their willingness to forgive such a grievous wrong. You say the adulterer doesn't "deserve" forgiveness? You are right in that for none of us "deserves" forgiveness and yet it was given to us...this is what makes it all so miraculous and such a wonderful gift and ability.
Yet for this reason I found mercy, so that in me as the foremost, Jesus Christ might demonstrate His perfect patience as an example for those who would believe in Him for eternal life. 1 Timothy 1:16