Is what you did with the hairdresser innocent...a smiple social interaction? There's a very simple way you can honestly answer that question: Ask youself this...would I have ever accepted that invitation if things with my wife were normal to good?
There is no way in HELL I would have accepted a man offer to go get a drink UNLESS I would have been able to bring my husband with me. Otherwise, no go on my end.
What if someone goes up to your wife at class and says "Hey W, I saw your H last night. He was at X having a drink with the cutest woman. I didn't say hi though. They looked 'busy'."
What's the difference between that statement to your W and what's been said to you?
Good luck to you Steve. I think if you really believe this: "I did not ask for this and I have done nothing wrong that would require this much of a fight for my marriage. I am done fighting. I would like someone fighting for me for a change." your ride might not be that long. It might just end pretty fast. Obviously there is something wrong with the marriage, at least from your wife's perspective. None of us wants to admit we were possibly a crappy spouse, but something has to give. Happily married people don't go outside the marriage.....