As long as your W is in denial about OM and is proceeding with the D, what is it that you need to do? You can not change the track she is on. She needs to derail that train herself.
All you can do is sit back and let things run their course. It is your choice to hang around and watch the train wreck and help pick up the pieces or not. Only you can make the decision if that is what is best for you.
I know, from my own perspective, how frustrating it can be to try and remain calm while someone I love is seemingly oblivious to the truth as I perceive it and hellbent on continuing down a self-destructive path.
Her telling you to go get a girlfriend is something I find amusing from the POV that it is likely to ease her sense of guilt or trying to justify her having an OM herself. Just my opinion... a conjecture based on what you have told us.
From what you have posted it appears as if she has detached herself from the kids. What the financial state of the OM is of no concern to you. That is his problem, not yours. It doesn't seem to be an issue to her. All the financial stability that can offer seems to be of no concern to her. She has her rose colored blinders on. She has to remove those herself... you can not snatch them from her face.
Hang tough, brother... Take a deep breath.
“Things turn out best for the people who make the best out of the way things turn out” ― Art Linkletter
