Yuck. You really need to set some boundaries. You are his wife, and this woman makes you uncomfortable- and for a valid reason. You arent telling him that he cant be friends with ANY women. That would be controlling. If you are not willing to enforce the boundaries, ie, consistent consequences, then dont even bother with them at all. That will make you look weak and you really need to be committed to this.
If this other woman really is more than a friend, then these boundaries are going to be about protecting you. Like someone else said, right now he is in a fog and logic will not sway him.
He is placing this friendship before his wife, and thats not healthy for a marriage.
I guess I gave the wrong finger to the wrong man...