Was I wrong to tell a long-time friend's now ex-wife that he was cheating on her?

A long-time friend of mine was cheating on his wife. He did not hide it and had his friends lie to cover for him. He kept saying he would tell her that he was cheating but he never did. He would bring the woman over to their house and even have her play with his/wife's kids while she was at work! I never told his wife (who was a good woman to hang out with but not like one of my best friends) as he kept saying he would tell her. But he never did. It was only when I had a conversation with his wife that I found out that he kept denying to her that there was another woman and that he had just fallen out of love with her. At that point, she said "Well, if he is out of love with me, what can I do? I guess I will just sign the divorce papers so that I can go on...I won't ask for any child support and I will just move on." At that point, I felt that she needed to know the truth. Well, as you can imagine, my friend now feels betrayed. I got into an arguement with the girl he cheated with and she basicallly called his ex-wife ignorant for not recognizing the signs of cheating and that the (Ex)wife should have known better (basically saying it was her fault for it getting so bad). All I know is that if my husband was cheating on me, I would hope that someone would tell me. At least I would know the truth. I am so annoyed by these 2 people and it has definitely ruined a long-time friendship.