The FBI was monitoring his emails written when he was still on active duty.
That does not appear to be correct. According to the NYTimes:
Government officials said that the F.B.I. began an investigation into a “potential criminal matter” several months ago that was not focused on Mr. Petraeus. In the course of their inquiry into whether a computer used by Mr. Petraeus had been compromised, agents discovered evidence of the relationship as well as other security concerns. About two weeks ago, F.B.I. agents met with Mr. Petraeus to discuss the investigation.
Petraeus resigned from the Army on August 31, 2011.
So this means he the affair, resigned from the Army to take the CIA position, knowing he had had a recent affair. Then "someone" notified the FBI to start looking at his e-mails "several months ago". Several months ago like September 12, 2012. Get the drift?
Finally, this gem from the AP
Morell rather than Petraeus now is expected to testify at closed congressional briefings next week on the assault on the consulate in Benghazi, which occurred on the 11th anniversary of the 9/11 attacks.