I will reread your post and think about this. I am in a very similar situation but further or longer down the line. I have stuff to say that I learned on my path that may help.
In the meantime keep posting.
I will say that regardless of whether you agree or find it fair, her perspective is her truth. HEAR her.
From your brief outline I don't think you are in lrt yet.There will be time enough for that later.
Although it is not where your focus should be, an EA will prevent any progress regardless what you do. I would want to know if I was up against that. My W did have an inappropriate friend, which I am sure did not help me. I snooped a lot to be sure it didn't develop. It consumed me.I decided to dig for proof and confront. I found only light stuff that would fall into a friendship so without proof I decided to not let this eat me up. Easier said than done. That friendship is no longer present but W is still not there .
IMO a M cannot thrive/survive if one partner is emotionally connected elsewhere.But breaking that connection is not the key, though it must happen to progress. We are all in this mess because we lost the connection with our spouses.ThThe key is to rebuild connection.TThat is slow.
Finally I wrote more than intended. I got to go. I'll check back in a while.Keep posting. The more info we have the better our insight into your situation.It will also help you as you have to think about your M deeply to tell us.
R 25 years M 14 years S11 & S13 Working on it alone since Oct 2014 M in trouble a lot earlier (~2 years) Feb 2016. 1st R chat in a yr. Next R chat Aug'17 Still together