know my brother did the deed because I saw him two times before I found out about him and both times he never said a word to me when I was talking to him and his wife about the problems
Wait. Seriously, hold on a minute. This is not evidence of anything other than difficulty talking about a very sensitive topic.
Your cheating wife told you this. Is it possible that it's another of her lies? One designed to not only really hurt you, but also to create a shitstorm that takes her out of the hot seat?
I think it'd be very wise to find out before telling the family.
As an aside, you're describing your wife--who had an affair in ADDITION to the alleged one with your brother--as "getting carried away."
No. ESPECIALLY if she had an affair with your brother, she did NOT "get caught up" in things. She CHOSE them. She is every bit as culpable as the men with whom she chose to have sex. Your brother is neither better nor worse than her, if she is telling the truth about him rather than attempting to deflect attention from herself.
My point is that you have a VERY mixed-up wife, and while, YES, if it's true that she had an A with your brother, the truth should be shared (because no BS should be in the dark, and really, if your wife has had more than one A, your SIL is at pretty high risk of contracting something--and should know to ask for testing), if she's yanking your chain to cause you more pain...well. I'd want to be as sure as I could be before confronting and/or outing the A.
Are you sure you want to R with her?
As for how to divorce a brother, it's not as hard as you might think. However, be prepared to be estranged from the rest of your family, because sides will be taken, and unless you divorce, your wife will make it VERY hard to align with you.
Do you want to spend the rest of your life in an Us v. Them scenario? Is your wife capable of being part of your team in a way that is not emotionally dangerous to you?
(Or is she spewing shit to throw you off your game because she's one sick cookie, who needs considerable IC before you even begin to consider whether R is even a possibility?)
In your shoes, I'd breathe. I'd tell myself I was married to a liar, and that her word cannot be trusted. And I would do a LOT of investigation before making a decision about whether this "information" holds any truth.
Because failing to discuss your wife's infidelity is NOT evidence of having an A with her. Many people are very uncomfortable with the topic. You have no idea, at this point, why your brother was. Maybe he's a BS. You don't know, because you are choosing to believe the word of a woman you know to be a liar. A woman who has motive for creating a storm. A woman who has knowingly injured you before, and may have no compunction about doing so again, if it makes her life easier, somehow.
Do some investigation. If the concern persists, ask your brother. Alone.
Then, consider telling his wife and family. IF it is true.
[This message edited by solus sto at 7:56 AM, December 5th (Thursday)]