Done with PMA? What do you mean? Even if you can't keep your marriage together and your wife doesn't wake up and realize what a destructive, mean, ugly shrew she has become, there's always a positive side to things... like now you don't have to live with the bit@h!!! I'm sorry, but any woman who wants to keep her children away from a father who loves them is evil. Ultimately she will hurt her children more than she's hurting you. This is not a woman you want back at this time. She would need to change. This should make it easier for you to detach and GAL. This OM is not "winning" anything if he ends up with your wife. She sounds like a nightmare. Let him deal with that....
And just DON"T FORGET to stay nice and DB in spite of her hideousness. Don't give her the satisfaction of you being mean or nasty back. Please!!!! I want her to regret this ugliness because eventually, at some point, even if years later, she will.
And the first thing you need to do is not blame yourself with this. This is one more thing you have to let go of. You are not responsible for the reality of the situation and what is occuring (and make sure at some point you let the kids know that.... tell them it was not your choice). How they react, what they feel... you are not responsible for this. Let it go... and let her deal with it. They are young now, but eventually they will understand.
Don't worry about looking like a fool or sitting duck in W's eyes. You don't. You just feel like one. When anger is high, I think your best bet is to go dark as much as possible. Maybe you can reduce communication to email and make it as business-like as possible. Speak with a lawyer about how you should be setting up custody arrangements during separation. Is she currently trying to keep you from seeing them? Perhaps she's a lot of "hot air." Don't worry about the inlaws. My FIL and SIL were pressing my H to divorce me as well (SIL even set up my H with dates!!!).
There is no arriving, ever. It is all a continual becoming.