How would your wife feel if the situation were reversed? How would she react, and what would she do? She knew what was going on, and did nothing to get out of the situation, so I strongly consider this to be cheating. And as someone else mentioned, there's a high likelihood of this not being the only time this has happened (although I do understand that you believe her at this point.) After all, she let this happen for a reason. How did you find out about this, did she tell you out of the blue, or did you come across some evidence of some sort?
If you and your wife stay together, this will obviously have far reaching effects on your relationship; when she's gone for extended periods of time, you will always have that nagging thought in the back of your head that she's off doing something inappropriate (or worse), and this will come out in flashes of distrust and jealousy, along with a greater amount of fighting between the two of you. You have also lost a certain amount of respect for her, and this will show.
Among frequent business travelers, there is an expression: "What happens on the road stays on the road." Be aware of this.
Good luck to you, whatever happens.