Seems to me your sister can save her marriage and her husband has hope. The reason is your Sister came to you. You understand the position of your brother and now you are gaining advice to help.
If your sister was truly gone she would not of told you. She trust you. Don't tell her what's right and wrong but validate her feelings like you would your W. Your role for your sister is listening validation and truth. I have a friend in the same ditch he is a WH and his W has treated him like deal their whole M. I just validate and listen and tell him the truth. I never tell him he's wrong.
I say things like your family is important and your W still loves you. And when he says, "yeah right", I say I get it. And continue to listen.
M:37 W:37 T:11 M:10 S17, S13, S10, S4 BD:06/28/17 OM confirmed 07/20/17 Recon the M 10/29/17 Working hard:2gether
Onward and forward
This process is not a sprint it's a marathon! Patience, Patience, Patience.
