I'm very sorry for the situation you're in -- the same thing happened to me at about the same time, although I had been married longer.
Most men in your situation are *very* surprised by what has happened and seek to solve it like a math problem. If you can understand what you did wrong, you can fix whatever it is and put things right again. We like to think that things are logical and linear, if I do "A" then I get "B", but unfortunately these situations are so complicated and nuanced, there is no simple thing you're going to figure out that's going to turn things around.
The first thing to think about is to surrender to the fact that there is no easy fix. For people who are used to solving problems, that's not trivial.
The second thing to think about is that there is pretty much nothing you can do to make your wife *feel* the way you want her to feel. She can't even control how she feels about things. What you should take solace in is that she didn't used to feel about you the way she does now, so that proves that feelings can change. Just as you can't point to one single thing that changed her present feelings, you can't do a few simple things that will change things in your favor either, it's much more subtle.
Third, realize what's going on with you. Chances are that if your wife was very unhappy with you, you weren't super happy with her either. When one person leaves, or blows up the relationship, the other person is typically completely stunned and feels totally out of control. Your own complaint list tends to go out the window and you will suddenly feel "in love" again and put your wayward spouse on a pedestal.
The bottom line there is that as the "left behind spouse" things are much worse than you realize, and have been for longer than you understand. Therefore, turning things around will also take much longer than you can currently appreciate.
Right now your wife resents you -- she resents you for things you did in the marriage both real and imagined, things you didn't do in the marriage both real and imagined, and resents you for making her be the "bad guy" by blowing things up. She also resents you for making her feel guilty about the emotional friendship she's developed with this other man. You're the lightning rod for her resentment.
Each move you make now needs to be measured against that yardstick -- will this make her resent me more, or less? If you make her feel guilty, she's going to resent you. If you make her responsible for your feelings, she's going to resent you. It's a very slippery slope you're on
Hey Tobias you are quoting this...but are you listening?