Donot let the sun go down on your anger, lest the devil get a foothold. Now that is in the Bible too.
That's only part of that passage, and an interpretation of the meaning. The more literal english translation from the first known English translation in the Cloverdale bible reads:
"Be angrie, but synne not. Let not ye Sonne go downe vpo youre wrath." Ephesians 4:26
The Jewish Bible translates that passage as follows:
"Be angry, but do not sine-don't let the sun go down before you have dealt with the cause of your anger."
The bible also instructs us not to repay "evil with evil" and that "a wise man is slow to anger", meaning we shouldn't take revenge or allow anger to control us. Not that we shouldn't get angry.
The bible is also full of the consequences of incurring God's wrath. Come to think of it, although it may be debatable, most theologians agree that Judas was not forgiven for his betrayal of Christ.
Unkess you have personally endured the pain of divorce as a direct result of the betrayal of infidelity, instructing another they should just forgive, would be like me telling someone with Crohns that they should just deal with the pain. There are some things which are just not possible.
I married my first husband right out of high school. We were only married a couple of years when I discovered not only was he cheating, but had actually moved his girlfriend into our home, and had her living in our attic.
I was depressed for months, and all I did was lay in bad and cry. I could barely function. Then I got angry, really angry, which gave me the energy, and motivation to get out bed, and take action to protect and better myself. That's when I started to heal. Yes, I forgave him, but that came a couple years down the road. I most certainly did not forgive him while him and his girlfriend were still trying to hurt me, because my anger is what was giving me the energy and strength to fight back. My anger was very constructive.
I couldn't find it my heart to just forgive him. To compel myself, I performed an actual act. His new wife needed an operation, but it was very risky, and as she was Catholic, their marriage was not recognized in the "eyes of the church". For the sake of their children, she didn't want to risk dying in sin, and wanted to get married in church first. Only before the church would allow it, his prior marriage to me had to be annulled, but the fee was $600, and with all her medical expenses, they couldn't afford. I didn't hear it from them, but upon learning all that from a mutual friend, I went to the Catholic Church, paid the fee, and filed for annulment--and I'm not even Catholic. I didn't give infidelity as my reason, but rather that I practiced birth control throughout our marriage.
I never said a word to either of them, because I didn't do it for them. I did it for me, so I could free myself from all remaining anger and resentment. It worked too. She's extemely religious, and tells everyone that she prayed, and God answered her prayers. For all I know, that may even be true.
To be completely honest, I didn't even come up with the idea on my own. I got it, of all places, from my ex! He wasn't remorseful at first either, and he and his GF did all kinds of evil things to harm me. I'm sorry to admit that I retaliated, not that it made me feel any better. When my ex finally came to grip with what he had done, he not only expressed remorse, but made full restitution, paying me back financially, for all they had "stolen". I didn't ask him to do that, but he told me that he wasn't doing it for me, but rather for himself. So he could feel better about himself, and heal. After he remarried, I decided that I deserved to feel better about myself too, and took action to complete my healing.
But I would never recommend anyone forgive during the initial stages of divorce, because those who do, usually end up getting taken to the cleaners, and regret it later.
Not getting angry, also sends the wrong message to others. If the only side of the story they hear comes from your ex, then that's all they have to go by. If you don't stand up and defend yourself immediately, the damage is done, and can not be undone later. That's the mistake my current husband made with his ex. He wanted to be the "better person", refusing to stoop to her level. As a result, to this very day, even his own family blames him for their divorce. Even though she was the one who cheated on and left him--for his best friend. She's been cheating on and leaving all her subsequent husbands as well, but regardless, even his own parents still believe the lies she told.