My brother married my best friend and they have two children. My sister-in-law and I have been close since the first year of high school and there is no memory from my teenage years that she is not a part of. She is a sweet and calm person who has treated me and my family in the best way.
I recently learned that my brother is having an extramarital affair. He asked me not to tell anyone and promised to break up with the other woman.
The last time my friend and I met she was very upset and when I asked her what was wrong, she told me that she and my brother have some issues in their relationship, that my brother is away from home for many hours because of work and when he comes home he wants his peace. He is constantly on the computer or on the cell phone and does not even pay the least bit of attention to his children.
I felt very bad and did not know what to say. I'm afraid that my brother will continue with his affair and I feel that I am making a fool of my friend by knowing and not saying anything to her. She could possibly save her marriage. But how can I ‘rat out’ my brother like that? What should I do? I feel terrible…
What you can do is talk to your brother for a second time. Try to share your concerns with him, without moralizing and without criticism. After all, no one knows exactly what is going on in the other person's home, what issues they may be facing.
However, when carrying on a relationship outside of marriage, it is very important for the individual to know what it is they want from that relationship, and how far they are willing to go. Contact your brother, discuss with him what he imagines to be the evolution of his extramarital affair, and what the consequences will be for him and his children if he divorces. Ask him how he would feel if it was his wife who led a double life, whether he would accept her hiding her true feelings from him and a fool of him behind his back.
Finally, tell him honestly how you feel. I do not know if he shared his infidelity with you, or if you were informed by a third party. In case he confessed to you, tell him about the burden he put on you, about how uncomfortable you feel towards your friend and ask him not to discuss anything about it with you again. In case you learned about it from a third party, let him know that nothing is hidden, and that since others have already found out about it, he will soon be forced to face the consequences of the truth.
As for your friend and sister-in-law, try to talk to her and find out if there are any problems in her relationship with your brother. Advise her as much as you can to treat her husband with love, not to be closed off by herself, but to approach him and try to keep her family together in every way.
I do not think it would be good to reveal to her what you know about the infidelity. This will not help in any case.
There is still a chance that your brother will return to his family and try to hold onto it, either because he will realize his role in it, or because he will be forced to, in case his relationship with the other woman does not go well. In both cases, there is a chance that the family will find their balance again and the couple's relationship will stabilize. But if your friend learns from you about her husband's infidelity, there is a chance that she will react in a way that will lead to a final rupture.
Even if she learns later on that you knew about it, after the initial reaction that may be negative, she will think logically and understand that you did it to keep their family together.