An attack of spew from your W. Now, this makes more sense (with regard to your letter) as it is a protection mechanism for your children. As I see it, your kids have made a decision not to see your W whilst she is 'involved' with OM. I'm no expert, but I can see this going two ways.
The first is that your W really doesn't care about the outcome of your M and has simply been cake eating whilst having some kind of R with OM. On this outcome, she will continue as she is and you will become D'd.
The second outcome will give a jolt to W, possibly pulling her out of the fog and a realisation that she is losing her entire family for the sake of some strange obsession with OM. This could lead to R (your choice) and a piecing together of the fractured family.
I do agree with you that while ever OM is staying with your W (if it be an EA, PA or friendship) there can be no R and you have every right to push for a D so you can finally have some peace and live your life, without worrying every day about W.
My last piece of advice, old pal, is to just hold tight for a few more days. Let the events of the past couple of days mature in your W's mind.
M 45 W 52 SD22 S9 D8 BD 6 April 2015 Not living together 4 Dec 2015
