Based on what you had written I had a feeling your wife was probably working through an affair. You may go into a roller coaster of emotions so be prepared. A wonderful book you should pick up is "Not Just Friends" by Shirley Glass. Here's a link: http://www.amazon.com/Not-Just-Friends-Relationship-Infidelity/dp/074322549X
It will help you understand the situation better. I imagine the reason your wife was avoiding sex was probably guilt over holding that secret in. The nice thing about these secrets being out is it deflates the whole thing.
There's a lot of guys on the piecing board who are successfully working towards better marriages following this type of bomb. If you get a chance go over there and do some reading.
The good thing is your wife sounds remorseful and also like she's trying to be honest without hurting you. I imagine your head is spinning right now. Try to take it easy and don't do anything, or react to any extreme emotions, without waiting a day or two. Hang in there! There's a lot of us here in this boat with you.
There is no arriving, ever. It is all a continual becoming.
