"As much as I tell her now that I'm willing to fight for this, I think she is pulling away"
Well, yes. This is totally predictable. The more you pursue her, the more she will pull away. She will do whatever she has to in order to maintain a distance she is comfortable with.
Doing what would work for women posting to the SSM board who are interested in working on their Ms and SLs is not going to work for a woman, namely your W, who has more than a foot out the door. But, she doesn't have both feet, yet. She was searching for "troubled marriages" after all. If you would give her enough space to breathe, she might choose to really work on the M.
In the meantime, focus on yourself and being a happy, confident, successful person regardless of what W does. This is all you can do to help your M until W is truly invested in working on the M with you. If you become someone she wants to be with, perhaps she will choose to really work on the M.
Have you read DR yet? You are obsessively focused on OM. OM is the least of your problems. Confront W on the A or not. Whatever. Getting rid of OM is not going to solve your problems (though forcing the OM issue may increase them.) OM is not the source of your problems. Getting rid of him cannot solve them. Draw the line in the sand wherever you want to, but do it because of where you choose to set YOUR boundary, not because of how you think W will react.
Other than obsessing about OM, there is plenty that you can do now to work on your M and yourself, work that you will need to do to be in any R successfully, with W or someone else down the road.
