If you knew your friend was cheating on her husband, would you say something?

A good friend of mine, told me she cheated on her husband with his best friend. Crazy right?! My friend still hangs out with her husband AND his best friend all together (same room or at parties), I want to tell her husband because I feel that it's so wrong but he shouldn't hear it from me. What would you do? 

Vote below to see results!