I feel for you but it sounds to me that she's done. And has been done for a long time now. Done with the comfortable life you have all been living. It sounds like she is making up for lost time sexually with this man. Perhaps all she needs is to blow off some steam and after the novelty has worn off she will be fine with working on what you have. Its not been long enough to tell I don't think.
I would hang in there for at least 6 months to a year and see where it goes. I would also be working on spending quality time with her to see if there is still a spark there. Date nights would be a place to start. Plan something you know she will like and ask her to get involved in finding new and exciting things to do without the expectation of sex. I would also be finding myself some really good sexual outlets that are not going to harm others. It might take awhile, so why not see what you can do about satisfying your self.
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