I am a big fan of Chapman's the Five Languages of Love. Could the statement that she is the only friend he can talk about his relationship with his wife, be a cry to you that he needs to have some quality time and conversation with you?
What are your husband's primary languages of love? Do they include "quality time?"
You are obviously very (and rightfully) angry at your husband for his affiar, but prior to that was he being told that you loved him in the languages of love that made him feel loved?
These are things you may want to think about once you have the situation more undercontrol.
Right now you are in divorce busting mode, but at some point you may need to shift into relationship building mode. When that happens you may want to have done some reflection on where things went wrong in your relationship and what changes you can make to insure this will never happen again.
Stay strong and good luck to you.
>43 years of marriage--My wife and I are now closer than we have been in decades. I believe that my SSM is over.