You sound so broken. Its sad. I want you to please remember one thing. It really does not matter how good of a friend/lover/spouse you are, this isn't about you. Your wife will desire additional partners because that's just how her brain works. I know it feels impossible but at least try not to take this personally.
What seems devistating at first often ends up being the best thing that ever happened to you. Maybe you'llne look back on this one day as being a turning point in your life. One you're evermore grateful for. Best wishes, OP!! : D