This is the first time I experienced the ability to tell another sim their spouse is cheating.
I started a new game and day1, my sim is playing guitar in front of the theater. About ten sims show up and after she's played for awhile, she decides to ask Rennee Littler for her autograph. After impressing Rennee, they talk until friends and when I go to "Friendly" for more chatting, I see "Tell Rennee that Rueben has another relationship". So, my sim did and Rennee cried and their friendship increased to Good Friend.
Has anyone been able to tell another sim about cheating?