You should tell her that the counselling is no longer required and that you will no longer schedule joint sessions. You won't tell her if you're still going to counselling, that's something you do on your own time and schedule and you keep it to yourself.
- no more pursuing - mo more chasing - no more gift buying - no more dinners - no more relationship talk - no more txts, emails, phone calls, voicemails, and heartfelt tear jerking letters
Are you getting the drift?
And yes it will be hard for you to do all of this but that is precisely why you must.
Yes let her go and let her do what she wants to do.
Tell her you know about the other guy and that you won't tolerate her having an affair, it's disrespectful. If she wants to do that, let her. She won't be sleeping in the master bedroom anymore, she can find somewhere else to sleep, she can let the kids know that she's having an affair, either that or you will, you will speak to the OM's wife and let her know about all of this too and we'll see how long he stays attached to your wife. Listen, in the end, you can't force her to be with you but you can't reward her actions either. She's a big girl, let her learn to live with the consequences. Start splitting up the money before she sucks you dry, get a new savings account and get your pay deposited in there. Give her a list of the monthly household bills and tell her what she's responsible for, 50%. She doesn't want to be with you, she doesn't get to use your resources. You will push for and get joint custody, trust me you will, and you will get it, don't be trapped into thinking you will get taken to the cleaners, that mindset is a self-fulfilling prophecy, fight for and ask for more and you will get it, I guarantee you this, don't settle for less.
Let her be with the OM. Tell her you want to be with the OM because you don't want to be with someone who doesn't want to be with you. And then tell her it's time for you to do the same thing, enjoy the company of a new female companion, it's been a while since you've been with another person and you want to find out what the big deal is since your wife thinks it's a great idea, maybe you will too ;-)
Everything you must do is the opposite of what you have tried, it's counter-intuitive, and yet these are things you must do.