My first thought is how very wrong it is for your mom to come running to you in tears when any of your siblings accuses her of anything. Triangulation! But secondly, I definitely wouldn't bring it up to your brother. If he has anything along these lines that he wants to discuss with you, he can. You don't necessarily have a clear picture from your mom of what he said, thought, or intended when he had this discussion with her. If your uBPDmom is anything like mine, she's capable of completely mis-reading a comment to the point it becomes nearly unrecognizable. And furthermore, even if your brother said, did, and meant exactly what your mom thinks he did, it's still not your business until he opens up to you about it.
Thanks for the response. Your advice, not to bring it up, is pretty much what I was thinking. I also had the same thought that she may have completely misread what he was saying since I know she does that with things I say all the effing time.
I'm not sure why she told me about it. Wanting to share her pain? Wanting to get her version in first? Knowing I was close to him and wanting to make that closeness strained so that I have problems with him like she does? I don't know... .The other day she did say something about how he and I being close was me rejecting her so I definitely have my guard up when it comes to things about him.