You can find your own way to word it, but the focus is :

1. This will fail - she's been warned by you who was obligated to protect her
2. Excitement is NOT happiness - You tried to help her understand the difference
3. You will NOT wait for this to crash - you are moving on and will be healthier without her affair in your life

THose aer KEY points you need to sign off with... worded whatever way you like..

Keep your ground and your dignity... ALWAYS

If you are HURTING TOO MUCH to keep your ground, keep AWAY from CONTACT...

STEEL yourself ... OR PROTECT yourself.. but do one or the other...

You NEED that right now in particular... divorce is HARD... you need to help yourself through that... surrendering to the affair is NOT gonig to help you through a divorce... challenging it and keeping your dignity is how you survive that.

There will always be better chances to kiss this affair good bye the way it deserves.