Petraeus is being set up as the Benghazi fall-guy. Extra marital affairs are matter of course for democrats...certainly tolerated if not celebrated.
No matter if he was pushed to resign, or he is getting out before TSHTF, or this is just a convenience coincidence; the memory of Petraus will be that the CIA is the source of "them movie made them do it," as well as any intelligence failure to know of the threat and to act in defense after the attack started.
Departed ones have very broad shoulders.
my guess, is that Obama’s people stated you go along with our side, in the upcoming investigation or we out you on this affair... and he probably said screw it, I won’t do it.. I’ll come out now with the affair, and resign..