Hi Twisted, I'm really sorry you've had to/you're going through this it's has to really hurt to be told something like that. I've got to say that your wife seems to have been really insensitive/disrespectful not to have discussed this openly with you a long time ago, but of course I don't know the whole story.
Regardless make sure you take the time to fully absorb this and decide whether you want to continue working on this with her. If you're going to decide on working through it, make sure that it's as much about you wanting to as opposed to feeling you need the relationship or the fear of loosing what you had (or the thought of what you had?).
So really important to let out your thoughts and your feelings and continue to talk about things. Although do you think a little space from her might help as well in you "getting your thoughts together"? And decide................?
You're right it probably would/will be really tough to get through something like this, as she's kept it to herself so long and it certainly wouldn't be your fault if things don't work out!!
But if you come to the decision that you want to carry on (I'd say walk away!! but you know the situation much better than me) then it may be possible to gradually put things back together. Skipping the doc, talking to a marriage counselor sounds like a great way to go way.
There may be backtracking over things that you've felt were OK in the marriage which may be really painful but there really needs to be a new approach to communication in the marriage, identifying and talking about problems/issues and finding a way to work together (non-judgmentally) towards finding solutions you're both happy/content with. A lot of listening, a lot of understanding, a lot of talking.
You're going to find a lot of stories out there on the web, and you might find some approaches useful, but just remember to do what's right for you, and if you continue with the marriage maybe find some ideas which are right for both of you. Every relationship is going to be different so solutions aren't always going to be a "one size fits all".
It might help exploring how things were before the relationship changed in her eyes though, and trying to bring back some of that spark, as well as figuring what went wrong and why. Can you retrace and re-enact some of the things that were really significant between you two back then? Bring back some of those shared memories, and the memory of how much you loved each other then? The things you loved so much about each other, which are probably still there deep down.
Things might not ever be the same again, but it is possible that this could make you both even stronger. And you will have shared/experienced a lot with each other in the time you've been together, that has to count for something.
Anyway, if you decide not to continue with this, or it doesn't work out, make sure that you don't "carry all the blame". Sure if there are any lessons to be learned from this you can take on to another relationship, absolutely do that. But this sounds like a two-way thing here, so it is just as much about her as opposed to you having done/been everything wrong.
And that's me being diplomatic and trying not to say what the **** was she doing by not communicating and talking about the issues and trying to resolve them before now!!
Alison