it must be a phrase that gets passed around from toxic friend to toxic friend, or pushed in women's magazines.....they all seem to know the words.
as far as the poor OP getting pilloried here for being beta...hey, it is who he is. we all feel sorry for the situation he is in, but a lot of the things suggested here...he is simply not going to be able to do.
If i ever saw a guy who was better set up to become a cuckold....it is the OP. he might enjoy that sort of lifestyle, and get a few more years of marriage out of her before they finally divorce. the story plays like a cuckold story already: "i read her smart watch about her giving the guy a BJ, and not regretting it. i was jealous, but turned on at the same time....and knowing her girlfriend knew all about it made me more turned on"
I don't think it will be anything that glamorous or titillating.
He's already checked out. She's already moving on,, at least emotionally and sexually.
What I foresee in his demeanor and response is they will both just kind of keep on maintaining the status quo and not rock the boat too much so as not to disturb their quiet and peaceful domestic life.
They will each pay lip service to "working on it" but each will continue doing their own thing including her banging other dudes and him trying to talk to her about the weather and when her car is due for a an oil change.
The first few dudes she gets with may not want her full time and so she'll stay in the marital home safe and sound for the time being while she loses weight and updates her wardrobe and gets her financial affairs in order.
I have the feeling he is much more detached and complacent however and he just kind of keeps on keeping on thinking that they are "working on it" and doesn't really do much of anything in the preparation for what is about to go down.
In time, whether it be weeks, months or even a year or so, she will find a dude that will take her full time and on a tuesday evening, like any other day, she will hand him a stack of papers and show him which lines to sign and which to initial and let him know that the movers will be there to get her stuff the next day.
My bet is that this will end with a whimper and not a roar.