Sub_Level
wants to fuck an Asian grill.
It's like ignoring someone being physically attacked because you're too concerned with your own safety.
What's wrong with that? And that situation is not even the greatest comparison because you can call the police for that. I don't know if you would call 911 to report infidelity.
Anyways, if OP is concerned about the fallout, don't tell, but I would stop being friends with the cheater woman and the other coworker guy. You can be judgmental and picky about who you associate with on a friendly basis.