He's responsible for his choices. He chose to cheat. He chose to crap where he eats. He chose of bitch of an OW.
If you chose to react by leaving, by going postal on both of them or by taking out a billboard, those would be your choices. Stemming from his choices, but still responses are your choice.
You're responsible for your choices. You called a spade a spade. End of story. Like how you choose to respond, how OW chose to respond is not your fault. She could've accepted it graciously as the truth and the pain talking. She could've owned her choices. She could've blocked you.
She chose to out the A...the A she was an equal perpetrator in. Not your fault. Had they not cheated there would be nothing to tattle about.
Looks like SO needs to own his choices more and lay blame for OWs actions on her doorstep.