Exactly what I came on to say Dele.
Would keep my mouth shut if it was casual acquaintances or work colleagues and I bumped into their other half out with someone else but for my mate mates I would definitely tell them and wouldn’t expect, or be worried about, any repercussions for passing the information on.
If you found out who had stolen your mates car or broken into their house would you just say “none of my business” and leave them to it?