OK, i am going to take a crack at helping someone, hopefully the ones with more experience can chime in, correct anything I may say wrong or whatever.
Here's what I see and some thing I can relate to in my sit. First, look at this. You said:
Quote: everything was fine until.... I asked her about how she and OM were doing.
I think everyone here will agree, from what I have read and in my own experience, never bring up the OP. I know it is easy to think and feel that the OP has a great deal to do with the problems. In reality it doesn't. Any and all the problems focus between you and her and in that, the only thing you can change is you. The OP IS NOT BETTER THAN YOU in anyway, so just put that away. If he diappeared off the face of the planet tomorrow it would not 'solve all the problems'. The problems would still remain and if she just needs someone around, there could be someone else.
I know it's hard brother, but for yourself, try to find a way to put the OP, A, or whatever it is out of your mind. Keep focusing on yourself, detach as much as possible and lower your expectation of what she will or won't do. Then do the hardest thing, wait. We can all wait together.
Here are a few things I do to help me mentally with my W's A. It may not help you, but I will throw it out there.
1- Marriage is more than a piece of paper, the marriage ended when one person 'decided' to leave it, after that one of those persons made a choice to date. This is no different than if a D was finalized.
2- In my case, for whatever the reason, my W still persues me while doing it, so I look at this as either.
A. He's not as good as me, LOL or B. She is just 'using' him to get over me and it's not working.
Both of these truly without lieing to myself, boost my ego.
I also regognize, lol, that now I am the one she is really having the affair with. Since I know about him, and he obviously doesn't know I am still around, who is now really getting cheated on? I know this is not your case, I was just hoping to show you some examples of how to deal with it positively.
You will just have to find what works for you, just find something where you can mentally pretend, it isn't happening, and then completely ignore it. It will help you and I 'think' it will also show her your strong maybe even making her guess, 'why isn't this bothering him'. I don't know.
As far as reading into what she is doing and not doing? I think we have all been burned by that one. My W looked like she was going to come back any second for 3 months and then I found out about A. One things for sure. When folks are doing this sort of thing, they are not really 'thinking' they are just floating around on there own needs and autopilot. So trying to figure out what they are thinking, although knwoing you need to know, seems only to lead to raised expectations.
I think you deciding to go dark may be a good thing at this point, because it will help you start really taking care of you and forgetting about her at least a little bit. It will also take you out of her equation and force her to deal with things.
Thats my 2. I hope I have helped and not hurt. Someone slap me if I have and join in.
Learn to laugh at it. People are people and everyone is human. Choose how you will act and don't re-act.