I think you are right in not telling your friend about the issues you and the husband have had. I think his behavior is normal, up to a point. He probably has no experience with addiction and doesn't know the proper coping mechanisms, so his first instinct is to protect his wife from everyone but him. He probably feels like no one, including your friend can be trusted, so he is entirely responsible for her well-being. He is probably scared and confused. I have been there before, and my first instinct was that I was the only one who knew what was needed, therefore no one else could really be trusted, regardless of if they had done something to merit my suspicions or not.
I think you can be there for your friend if she contacts you, and I believe that she will. I think the best for this situation would be for the two of them to attend some meetings, therapy, or rehab so that not only her issues can be dealt with but hers as well. He is going to have a rude awakening if/when your friend gets tired of him trying to make decisions for her, and your friend will never properly start recovery if she hasn't made any of the decisions herself.