All these lofty claims of “she deserved to know” and “I’d want to know if it were me”
Who is anyone to decide what a complete stranger deserves in this situation? Or whether anyone else wants to know? Maybe she is the kind of woman who doesn’t want to know. Maybe she’s made her peace with the kind of guy she is, but as long as she isn’t directly confronted with it, she’s happy to be kept in the dark.
If my husband was cheating I’d want to know. What I definitely wouldn’t want, is a message out of the blue, in the middle of a really stressful lockdown, from a complete stranger claiming they were exchanging messages with my husband.
If OP wanted revenge, she got it. If she was genuinely concerned about the wife, perhaps having a look on her FB to see if she could link to a good friend or relative of the wife and letting her choose whether to give the news. Not that I’m suggesting she should have done that, still a shitty thing to do, but it would have shown she was concerned about the wife.
What you want/need/deserve is not what someone else wants/needs/deserves.
And to suggest doing nothing is some sort of sop to men to let them do what they want is ridiculous. It is respecting women enough not to automatically assume they are weak and stupid and need someone else to save them.