With all due respect, Barry:

I owe it to her when she says there is no one else.
I disagree. You owe it to YOURSELF to find out. (And not by asking her. If she's cheating, she's also lying. Because cheaters lie.) And you owe her nothing right now. She has fired you as her H. What would you "owe" a boss who fired you?

We've been together all our adult lives and I have to believe she's still in there somewhere at the moment. It's not that I don't think she's capable of lying (or at the least, withholding the truth), or being a *****, it's more the already cheating part I can't (or yes, I admit..don't want to) believe.
She is in there somewhere. But you being a sappy doormat isn't going to help bring "her" out. Please don't kid yourself: Everyone is capable of lying. Everyone is capable of cheating. And you don't have to believe it - or even want to believe it - for it to be true. And regardless of whether it's true or not, your goal is the same: Stiffen up your backbone and go GAL and some freakin' confidence, for goodness' sakes!

I'm not trying to be rude, Barry, but your posts are dripping with sadness and despair. If we see it, W is seeing it. And that's NOT attractive. It's pitiful. If you're THIS sad - even without confirmation of an OM - I'd hate to see you with knowledge of an A!

It just hurts me to the core that she is just ready to throw our M away like this and not fight for it like I am.
From where I sit, you're not fighting *at all*. You're laying down and playing dead and waiting for your W to come around when she's probably - I'm sorry to say - feeling quite free and liberated. Those two things (you playing dead and W coming back around) will never go hand-in-hand; it simply doesn't work like that, Barry.

I think that's why I'm finding the detaching so difficult (she's not)
There's likely an obvious reason for this, but we need you to pull your head out of the sand to see it.

And NO MATTER WHAT, your course of action is the same!

Barry, PLEASE get back on your feet, brother. You're making me feel gloomy and depressed just reading your posts.

Your GAL efforts have, thus far, been to win W back. Please don't think that's going to work. GAL is to get you feeling better about YOURSELF. And I can tell from your posts you feel like a beaten dog.

No, sir. Pull yourself up by those bootstraps. Go do something really, really FUN! Do you like adventure? Jumping out of airplanes? What's something really adventurous you've always wanted to try? Rock-climbing? Salsa-dancing? C'mon. Gimme SOMETHING you've always wanted to try ...

... ??? ...

Now, go DO it. (And don't forget to come back and tell us all about it!)

M: 40 H: 44
Married 14 years
S11 & D6; D20 & D19 from previous M
2BDs/PAs, 8 years apart
Piecing: April 2014