That has to be one of the most ridiculous excuses for resignation ever.
Not really. Having an affair (and being found out) can pretty much destroy your intelligence clearance, because of the potential for blackmail. You don't get much higher clearance than the director of the CIA. Plus, from what I know of him (secondhand from a few friends/colleagues that have met the man), Petraeus is a good guy. If anything, he was probably holding this until after the election to keep it from becoming a problem for the administration before the election.
As much as I'd kind of hope for a Petraeus run in 2016, I don't see it. Everything I've ever read about the man says he has no aspirations to political office.
It's a damn shame. I thought he was our brightest general in the field in Iraq, and then in Afghanistan, and I liked him a hell of a lot better as CIA Director than I did Leon Panetta. I was hoping maybe Petraeus would become SecDef second term, but I guess not.
EDIT: Gaaaah, and already hundreds of dumbasses all over the Internet are screaming "It's all about Benghazi!". As if the
Director of the fucking CIA is going to make up having an affair in his resignation, to "cover-up" a relatively minor event. If this was a forced resignation (or even a voluntary one over some internal political conflict), it'd have been the standard "spend more time with the wife and kids".