My wife had a friend that was a semi pro bowler. She invited her to a tournament in Reno. While there my wife found out that her friend had an affair with another bowler previously and was screwing around with another dude during that trip. Apparently everyone at those tournaments screws around. The guy her friend was with previously tried to pick up my wife.
Anyway, the tournament was recorded via webcast and the friend's husband was watching. Nothing incriminating, but he did notice his wife hanging around the one guy a lot. One night before they flew back the husband asked my wife if anything was going on, that he was suspicious. My wife basically spilled the beans. The flight home was apparently very uncomfortable and when they got back the friend and her husband basically started blaming my wife for the whole situation.
So my wife ended up losing a couple friends because she got blamed for trying to ruin a marriage. Especially since the friend ended up pregnant (don't know who the father is, guess the husband didn't want to question it).
So again, no good will come of you saying something and potentially some bad could come of it if you say something.