I agree with betterm. If you want to expose and you think it will work, then just do it. Giving them advance warning takes away the element of surprise.
Okay, because you're an obviously intelligent womam and because I think you can take it, here's a 2 x 4 coming.
You still want your M to work and the fact that you're in so much anguish over the fact that H and OW had sex after he was supposed to have ended their A shows that you still feel for H.
You are now spinning. I have been there. I have done all the things that you have done - except exposing the A and speaking to OW. I can tell you that it doesn't work. Spew, threats and screams only serve to push your H further away from you.
Take it from me. I did that during the 2 attempted R before the D and look where it got me. In hindsight and even now, what would pull x nearer to me is what is advised here on the boards. Validate, stfu, state boundaries civilly but calmly.
I am not saying that your H is in the right. He's not. He has his head up his a$$, which means that you cannot expect him to think and behavd like a rational adult.
The onus is on you to be the rational one. It svcks, it is grossly unjust but there's no way around this.
I have to tell you now that whatever interactions you have with your H now will not help your cause. It takes time for them to emerge from the A fog.
Sara, it's probably better for you to minimise contact with your H until you can stop spinning and take control of your emotions. And plan how and what you want to do.
Have you read through the threads in Cadet's welcome post? Especially Sandi's rules and going dim and validating.
It's not easy but the training that you had to undergo to become a MD is not easy too. Draw on that same determination.
You can call me Dory/ Grl.
As a wise fish once sang,"Just keep swimming!"
It's no use to go back to yesterday because I was a different person then.