Chances may be slim on this, but sometimes a spouse who wants "out" may try to pull this as a valid reason to split, even if they know it isn't true. They convince themselves that you cheated and they are right and then they are "out of there" while maybe they always wanted to be, sounds far-fetched but it is possible. Also has there ever been anything that you have done to make her feel you were a cheater?? It's hard to believe there was never anything, even if to most of us seems very small and insignificant. Such insecurities can be brought out of the "closet" with triggers (though some people believe "triggers" don't exist) if your wife was having self esteem and insecurities problems for the 13 years you were married didn't you recognize it? Did she realize it? Was anything professionally done about this at that time?
It seems someone had needed therapy for a long time and never got it resulting in this outcome, "someone" may have meant both of you. It is good though that you are going to try counselling, it may help but if your wife is as serious and so eager to accuse you of false things and had unstable behaviour I'd suggest she sees a psychiatrist, he may be able to help her better than a counseller plus he/she can try some medications that may be of some help to her. Just my 2 cents, I almost did what your wife is about to do, I even had more reason to believe there was "hanky panky" going on, this woman(slut) travelled all over the world with my husband, air travel,eating and taking in the sites besides working together, etc.you know sooner or later someone starts to become attracted, and then "lie" about one's where abouts start, that's when a spouse almost goes balistic!!! It's the "lies", breaking the trust of two people who took vows when they got married, then some just toss it out the window for a "piece of ***".
Please know I am not accusing you of this but want you to see how a person can be made to feel. when betrayed, or am almost 100 % sure about it.
I wish you both lots of live and luck, take care now.
"darkeyes"