Most Helpful Guy
You NEVER fukkin' tell. Period. It serves no purpose other than to unload your guilt onto them. What a prick-of-misery thing to do.
However, most affairs are found out, some way or other. A lot of it depends on how close you are with the primary spouse - some are oblivious and deserve to be cheated on anyway. It's still wrong, you should just bail out if you're gonna fuck around.
Most Helpful Girl
I think those old movies/TV comedies said it best
although I'm speaking vicariously
those friends that fell into temptation did not fare well after confessions