You have the receipts, but before you act on anything, you have to determine how reputable that evidence actually is. There's always a chance that there was just a misunderstanding, Dr. Bonior says. You could be hearing this information fourth-hand, or people might be spreading malicious gossip about someone on purpose, she says. Of course, if you're seeing someone on a dating app first-hand, that's pretty indisputable, but it's always worth it to consider that there might be more to the story. Perhaps your friend decided to go on a break with their partner, or maybe they opened up their relationship on the DL. The bottom line is: Don't do anything until you know the proof is legit.