I guess the only to force a stop and ensure a stop to the affair is to expand who knows about it. Is it enough for me to confront my BIL, do I tell my wife she needs to have a sit down with my sister, or do I just tell my sister? Each of these would end the EA for good, but some will have additional fallout. Either case involving my sister will have the most fallout, of course.
You cannot depend on your wayward wife to have an honest heart to heart with your sister. The only way you should even consider your W telling her anything, is for her to do it in front of you. Otherwise, she will put her own twist on it. You cannot trust a cheater. In this case, there are two cheaters in the family.
By confronting your BIL, are you thinking he would agree to end the A and would have no future contact with your W? Do you see this as a way to avoid hurting your sister?
Is your BIL aware that you know about the A?
I understand you want as little fallout as possible. Honestly, I don't see how the four of you will ever be able to be around each other again. You and your sister, or you and your W, but certainly not the four of you. Even if your sister was not told, don't you think she would want to know why your W never went around her anymore, or why you and the BIL acted strange around each other? Do you really think you could go to family events and see your BIL there.......or see him and your W together in the same place? Your parents will know something is out of kelter, if this is covered up. Eventually, your sister will learn the truth, and then she will be angry and hurt at you for not telling her.
There just doesn't seem to be an easy fix for this disaster. I am so sorry for you, your sister, the kids, and your parents.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!
