She is cheating on her husband, would you tell?

My husbands best friend is a really genuwine nice person. Hes a really cool guy and has always been good friends of ours. His wife on the other hand is like those naggy women who are constantly yelling at there spouse. She criticizes on everyone, gossips all the time, yet calls herself a devoted christian. Our husbands are deployed and i am aware that she is having an affair with her ex. I know its none of my concern but to be honest it upsets me, most likely because i dont like her as a fake person she is but her husband is a really good person. I feel like telling my husband and maybe have him hint on to his best friend but i feel like thats crossing the line. Any suggestions? Or should i just mind my buissness lol thanks!