She has already told me she has cut off communication with the OM and that it wasn't about him specifically. It was about the feeling she had with him and that she didn't have that with me and hadn't for a long time. It gave her the confidence to speak up and finally say she was done. I feel so stupid that I was so blind and deaf for so long.
An in-house separation is on the table. I said I would sleep in the basement while we figure out how to sell our home, etc. I just don't know that it's going to help or that she is going to be willing to give it another try, regardless. I guess all I can do is stop acting like a lost puppy, stop following her around or trying to win her back. I need to make changes and do it for me, while hoping she realizes what she's doing. This sucks....
Are you offering to sleep in the basement for her, or for you?
You can overcome this, whether she can is a different path that only she can take, but you have to keep your mind right (calm) about every step you take and plan on taking. Your biggest challenge is keeping her close (presence) and being visible while you find your confidence to tackle your hardest questions... why am I like this and what do I really need in order to align and balance my life... but as you work on this it needs to be shared without words because they mean little, actions count.
You've attended her IC and it sounds like you haven't really invested in the value, but now it's time to stop looking at that forked trail and choose your own, like yesterday... but tomorrow will do. To make an impact you need time to slow the separation down so get an appointment with a counselor and let her know you have done so. I will share from experience, and your milage may vary, but I actually settled on a female counselor for this because I needed, as it also sounds as you do, to understand the perspective you aren't and an opposite-sex counselor may deliver that better in a way you need to begin hearing. This I share from my own experience and emerging path (11 years young in my own journey).
You sound, and I'd gather, feel thirsty from your wandering... you won't find emotional water in an oil well of logic that hasn't connected you spiritually to your wife.
The immediate calm is an important thing... it's what you do today that counts. If she see's that effort and you see a softening... put it aside for now, you are doing this for you as that is the only thing you can control but definitely let it assist you as feedback that you are on the right path for you.
Some are not successful as many experienced posters here shared, some can overcome and still be dealing with the ripples of a thousand past bad decisions for years, decades even, but once you are on your path, never quit trying to apply an eightfold path mentality to life and build your life on emerging positives that even if you are not successful with your wife, your children will be strengthened with.
Sometimes an unfamiliar path of self can lead you to the best places... do not hesitate and strap on your mindful hikers.
Peaceful trails be with you...