TEll her

Casadena

Dear Prudence,

I had to go out of town for a work conference for a couple of days, and had my brother come over to feed and walk my dog. As it turns out, my porch camera revealed that he’s been cheating on his wife—his mistress showed up at my house! Even worse, I could see that she is visibly pregnant. As if that wasn’t bad enough, my sister-in-law is weeks away from giving birth to their first child. What the hell do I do?

—My Brother Is a Bigger Dog Than My Actual One

levioosa

So brother is an asshole AND an idiot. 

charlotte989875

Your brother sucks, tell his wife. And show her the video. 

MyNameIsNot

"Bro, you have 5 days to tell Sue, or I'll tell her for you. This is not a secret I'm willing to keep, but it is something that I think should come from you."

Save the recording and change your locks. 

CharmedPam

Yup, his wife needs to know. I like the “you have such and such time to confess” route

banana468

Big fan of the ultimatum here.  He gets to tell tell his wife or she'll be told.