Oh oh. This doesn't sound good. I don't blame you for wanting to tell people, but this is too close to home for several reasons:
1. It may lead you to eventually build resentment over the fact that the best friend is more accepting than your wife.
2. This is not fair, since the best friend is not married to you. If she were, she might have a different reaction.
3. After your wife finds out that you told her friend, it may lead to your wife feeling as if you don't care about her feelings. She may also feel as if you are sharing something intimate with a woman that you are not married to.
4. It may cause a rift in her friendship with her friend.
One of the most important things to agree on, with the CDing, is the degree of outedness. After the best friend leaves, I suggest you have a long talk with your wife and discuss thoroughly who should know and not know. I also think you should tell your wife that you told her friend, since it is likely that the friend will let on at some point in the future that she does know.