Disappointing, but I am wonder what is happening behind the scenes. The FBI counterintelligence unit doesn't get involved when some official is banging some piece on the side. Are they concerned about possible leaks, blackmail, etc.? Do they believe there is a national security risk? Both individuals were US citizens, and Paula Broadwell certainly doesn't appear to have hostile intentions towards the government. Why the FBI counter intel is involved is something we may never know.
Speculation about avoiding Benghazi inquisition is just that...speculation.
Overall, I think Petraeus is a great leader. His contributions to this country should not be overshadowed by this, apparent, lack of judgement.