Hi Confused
I'm sorry you had to find us. I've tried a dozen times to respond to your post and I've not been able to find the words. You sound so much like me, four years ago.
I had all the same questions - why, when, how, why is it so much better NOW, etc. The one about admitting failure really struck a chord with me. I think that's what drove me - THAT, and not letting the OW "win". I worked my ass off making things right and meeting every one of his needs. For awhile, he worked pretty hard too.
His working on it is where my marriage failed. He quit. He blamed me for not trusting him, for not believing in him, etc. etc. What he failed to factor in to the equation was that he wasn't trustworthy when he was still breaking the NC rule. He always made jabs about not being able to live under my microscope, that he couldn't feel bad forever, and that maybe we just weren't meant to be because he didn't love me like he should. The day we divorced, he said he finally knew that it wasn't me torturing him, it was his own guilt.
Your H has absolutely got to take responsibility and realize that he is going to have to help you work through this. It won't be pretty. It won't be easy, but if he's going to ask for your trust, he has to show you that he deserves it. You will have those questions - and you'll keep them until he can help you put every one of them to rest.
My parents divorced when I was 13, too - due to a string of affairs.

When I started w/my therapist, she said, "THAT is why none of this looked that weird to you! You lived this, growing up." That was a big turning point for me. A good C can make all the difference in the world!
Try and keep from asking questions
right now that you don't REALLY want to hear the answer to - and if you do, try not to lash out when he's honest. I'm not saying put your head in the sand, fiddle dee dee... I'm saying that you have to pick your battles right now. It's an extreme amount of "stuff" to take in, you'll tackle it when you're ready.
Another thing I struggled with is "What will everyone say if I stay?" Well, with all due respect, who cares? I thought there was something worth fighting for, worth working it out for... it was, afterall, my life. Those who love you will understand. Plus, there is always the issue of wanting to do EVERYthing to make it right - so you have no doubts either way.
Hang in there. It might help if your H read here, to see where you're coming from with all your concerns. Email me, if you'd like. The good news is... yes, you'll eventually feel better. Yes, your self-confidence will return. Yes, there IS hope!
Monica
This is your life. Are you who you want to be? ~ Switchfoot