Dear ###,
I am sorry to say that I have secretly found out that Mr. ##### is having an affair with Miss #####.
My first suspicions came when I saw them Frenching in front of her house, and then I knew for sure when they went skinny-dipping in Mr. #####'s swimming pool, giving each other hand jobs while you were taking a nap on the front porch.
Why am I telling you this now?
Because you're such a good friend.
Take care, pal.