WIBTA if I told my brother that our dad was cheating first before our mum did what she did
When my parents split my brother ended up fully on my dad's side and stopped speaking to my mum completely, and the reason he feels the way he does is because he was told that my mum had an emotional affair and that was what ended the marriage. As far as he knows she is entirely responsible for the family falling apart and my dad is the person who got hurt.
What my brother does not know is that my dad was physically cheating before any of that happened. I only know because I was home one day and heard it, and my dad has no idea I know. My mum found out about it and her emotional affair came after that, but none of that context ever made it to my brother.
What makes it worse is that my dad is the one who has been keeping my brother angry at my mum, telling him she destroyed the family while leaving out the part where he was sleeping with someone else in the house while she was home.
I have stayed quiet because my parents are still going through divorce proceedings and my mum is worried that bringing this up could affect things financially for her. But watching my brother refuse to speak to my mum based on a completely one sided version of events is getting really hard to just accept.
WIBTA if I told him what I know?