Infidelity Statistics - Truth About Deception
I have a lot more problems with Petraeus' sharing classified information than with his marital infidelity. That seems more of a problem between David Petraeus, Holly Petraeus and their kids.
We also do not seem to know that much about what kind of classified information the mistress/biographer had. A biographer would probably have access to some secrets that the rest of us would not.