Two big things jump right out at me. They do so, because I can identify so very much with what you are saying and going through. More in a minute.
I've become a much more spiritual person through all this, from reading may kinds of spiritual books. I mean spiritual, not churchy. Bear with me. I learned that most of my problems have been caused by my assuming that all the rules in my life were right. I gravitated toward one philosophy that has 4 simple rules, 4 agreements that you make with yourself. A very short book called "The Four Agreements" sums it all up. Another simple but not easy transformation. The for agreements (here is where I bring this back to what you said) are to 1)Be impeccable with your word 2)Don't make assumptions 3)Don't take anything personally 4)All ways do your best.
First, replace every time you said "I thought" in your last note with "I assumed". The problem with assuming is that you are mind reading. You have no idea what she is thinking, and the only way you will know is to ask questions and find out what she needs from you. Of course, that means that she must be "impeccable with her word", always telling you the truth and saying exactly what she means. You can't control that, but you can try not to assume.
Second, I'm sorry if I said anything that makes you feel defensive. First you must know that when ever I pointed out how people can fail to live up to what might be interpreted as their responsibilities, I was talking about me. I failed miserably. I assumed, I avoided, I failed to follow through. I assumed that if there were no explicit complaints, everything was fine. I assumed that silence meant she had nothing to say. I assumed that spending so much time out meant that she was happy in her life with her friends. I assumed that I was off the hook. How wrong I was. Again, if you feel uncomfortable and defensive about what I said, I'm sorry. But I need to point out that you are taking comments I made about me and my marriage quite personally. It's good that you expressed that, so I could clarify.
Finally, I am very guilty of not doing my best. I allowed a lot to slide, and failing to receive direct complaints, I assumed that the meager attention I paid to the marriage was enough. So, I simply did what I thought was enough instead of doing my best. I have suffered long for these oversights.
On the other hand, I am not totally to blame. My wife is a classic conflict avoider. She will not express her complaints or opinions if she can avoid a conflict, no matter how minor. This is a problem that can be well handled in MC, but it needs to be identified. The last thing W would express was a desire for MC, because that could lead to conflict. The last thing she would do was nag excessively, because it DID lead to conflict. Finally, she had to complain to someone to let off the steam of all the pain she felt, and that happened to be her "friends", her divorced and separated bar and club and sports buddies who encouraged her to end it all and move on, and the sly, supportive and empathetic OM who was more than happy to lend a sympathetic ear, and a friendly arm around the shoulder. He was the friend I had ceased to be, and he was able to replace me. I say sly and I want to imply that he is evil, but he's not. He was probably as surprised as I was about what transpired. I know him. He is a nice guy, everyone likes him, he is fun to be around. He is also alone and lonely and nice and all that. This was not a plan, but the result of two lonely people coming together.
Our marriage was to W the epitome of what was not working in her life, and her relationships with all these folks, including OM were examples of what did and could work in her life. This is what I mean by her desire to stop what was not working, and to do more of what was. She got the concept way before I did.
This is how I've come to understand my situation. Most of the time when I write about what could have happened, or speculate about what did happen, I am talking about my situation in the context of another. I do not mean to accuse anyone of anything, but instead I'm trying to explain mistakes I've seen by virtue of my own experience. If you see similarities to my stories in yours, well I hope it helps you understand.