How would you react?

Ladies! Suppose you hear your SO talking to a friend who admits they recently cheated on they're girlfriend and is bragging about it. Your SO laughs asks a few questions, eventually changes the topic as tells you about it later. How would you feel about your SO laughing about it or not telling the friend what he did was wrong? Would you take it as a character trait to watch closer and be upset he didn't tell his friend it was wrong? Or would you not think too much of it and dismiss it as regular guy talk? Also if you were told about the situation would you find a way to tell your SO's friends GF?