Yeah, I am in the same camp as Ca3799, for now. I cannot comment on the infidelity, but regarding the unhealthy marriage, I had a few years (10+) where we were in a passionless, room-mate-like marriage, in the service to our two small kids.
In the early years of this timeframe, I did try many times to address the emerging lack of interest in the marriage and in me. I assured her I was still interested in her, and asked if there was any problem with me. Her response: “I don’t know”. I assured her many times that I was willing to work on things and make changes in myself and my behaviors, and asked if she was interested in doing that. Her response: “I don’t know”. Once in a while I would say something that would set her off, and I would apologize and ask if there was a better way for me to say what was on my mind. Her response: “I don’t know.” I told her that I felt like we could do better, and she told me “If you feel that way, you need to fix it.” This all taught me that my opinions, views, and needs were all extraneous issues, and I became just another mouth to feed. The room-mate. I gave myself the nick-name “Paycheck”, because that felt like the only reason I was kept around.
I changed my outlook on intimacy – I changed my expectations and taught myself that what I wanted in the bedroom did not matter. I stopped wearing the wedding ring (as did she, for the same reason as the OP). I told myself that all that mattered was staying the course I was on, no matter how shitty, because I did not want a divorce (having seen what it did to several of my friends and their children), and that in a few years I would be able to walk away with less impact on everyone, as long as I stayed the course. We did try counseling, as several in this thread mention, and it really did not help at all. I am sole-breadwinner, so I have more to lose in the event of a split (e.g. permanent alimony), so I nixed the idea altogether for a host of reasons. I decided to enrich myself and my life by pursuing things that made me happy as hobbies, as opposed to dwelling on the problems with the marriage. I could keep the status quo for a while, be with my kids, and keep everything stable, for everyone. I lived like this for years. I accepted my fate and gave up on improving things.
A few years ago, she decided she was interested in me again. I do not know what prompted it. She started taking care of herself better, got rid of all the mommy clothes and bought nicer outfits. She wanted to go out more, do things with me, and actually listened to me once in a while. Unfortunately, this upswing in her interest coincided with the death of my parents over a couple year span, so I was not a good partner at that point.
Today we have reached some sort of détente. The status quo is better now than back then, and the kids are bigger and less of a demand for her. Things are manageable, and there is less conflict and more fun between us. I am starting to remember the one I married, but we have a ton of work to do to keep things good, and make them last.
My point of this ramble is that no matter how shitty your situation is (unless there is violence or substance abuse in the equation), a stint in the marital doldrums can be overcome with time, and not being selfish – you just have to keep focused on staying the course, if that is what you want.