It is awkward to interfere in another person's marriage.
Frank sees Eddie cheating by making out with another woman at work.
Frank wants to tell someone what he saw.
Frank calls his own wife and tells her that coworker is cheating and that he just needed to tell someone.
Frank calls Eddie's wife and tells her that her husband is having an affair with a coworker.
Eddie's wife never knows the bad things Eddie did and dies in blissful ignorance after a long and happy life.
Eddie's wife is horrified and murders Eddie once he gets home.