Should I tell best friend her hubby's playing around?

A very close friend of mine has a dream life from the outside - beautiful home, gorgeous kids and enough money not to have to worry.

- Dear Coleen

However, I know her husband is a total player and I've heard he messes around with other women. What's even worse is that her tight group of mum friends know about his flings through their husbands, but haven't said anything to her, they just talk about it behind her back.