Should i tell her?

Iv gotten really close to 1 of my husbands friends wife, i was a bridesmaid at her wedding late last year. My husband has told me recently that before they got married he was cheating with a couple of other women. My husband told me that he was considering calling the wedding off to be with 1 of the woman but decided not to because they have a little girl together. iv been asked not to tell my friend because her husband would know that the info had came from my husband. i dont know if i should tell her or not. i thought maybe he had changed his ways now they were married but recently at a night out he dissappeared with 2 of the other guys and my husband said its because they like to go searching for other women. i really dont want to break up a marriage or get my husband into trouble with his friends. i just dont know what to do. i wish he had never told me.