so sorry to hear about this. You must be heartbroken. People cheat for different reasons. I tend to feel that they are really not happy on the inside when they cheat, or they feel something in thier life is missing. Has she given you a reason for her behavior?
Also did you think that this may be her way out of the organization? The reason I say this is we had a guy in one kh I was in who did not believe the org. had the truth anymore. He wanted out in the worse way but new his wife would not go along with it. He did not want to go out as an apostate so instead had an affair to get kicked out as an adulterer. This let him off the hook for having to do anything with "the truth" and he was able in a way to save face. He also thought if he changed his mind later, he could get back in easier for being disfellowshipped on the adultery grounds then on the apostacy grounds.
I know this sounds strange but sometimes people are desperate to get out of the org. and I have seen many crazy things done to do it. Like the saying goes "desperate times calls for desperate measures" Just a theory. Lilly