CF, You've been in an A for almost half your marriage. I wonder if perhaps you would be ready for what marriage will be like without the A going on - even without all the hurt that ending an A implies.
Maybe you could see an individual therapist for you first, before you bring everything up to W and before you decide to leave... just so you can figure out how you'll deal with this heart-ache and terrible secret at the same time. Also so maybe you can find out why you had the A and if you want to try to save your M. Don't act on what you're feeling right now.
May it be eternal while it lasts.
My sitch
Me: 36
H:34
M: 5 years
Bomb: 03/14/06