Have nothing to do with the fruitless deeds of darkness, but rather expose them.
-Ephesians 5:11, NIV
Usually, people who have never experienced being lied to and cheated upon for months or even years do not get it!
They might think the faithful spouse better off not knowing the truth about the betrayal. But I do not see that as an option left for those who seek to follow Christ.
We are to expose “the fruitless deeds of darkness.”
It is true that knowing about the lying and cheating will likely drastically change the relationship dynamics within the marriage. But that does not mean the better option is to continue with the deception!
And make no mistake:
By not telling, you are party to enabling the cheater’s lies.
That said, do not be surprised if the cheater becomes enraged upon finding out who told his or her victim about the cheating.
You are taking power away from the cheater by exposing the truth.
Exploiting a faithful spouse becomes more difficult when the adultery victim knows he or she has been used and played by the cheater.
Plus, it becomes more difficult for a cheater to play the victim or martyr once it is known that he or she is a liar and cheater.
Also, the faithful spouse might stop believing they were the problem knowing the real reason for the disturbance in the marriage–i.e. the lying and treacherous cheating.
My point is that the argument against telling a faithful spouse is a weak one, IMO:
Not telling someone is like a doctor not telling their patient that they have terminal cancer.
Not knowing does not erase damage done and the peril present.
It just gives the victim or patient less control and options going forward.