[Bazic606]

There are a few things that you can do to clear your doubts:-

1. Spring a surprise lunch during her office hour, just say that you happen to pass by
2. Tell her your schedule and let her arrange hers around yours, then make sudden changes to get her to change hers
3. Yank her away to a long holiday and watch her reactions closely
4. Go on an oversea trip and return a day or two earlier
5. Notice her change of dressing, perfume or any abnormal habits

In due time, she will probably leave obvious traces of infidelity if it is true.