By the time you're in the position Petreus is in, you don't have a conscious. The CIA is alot more powerful than most people know. There is no way in hell he willfully admitted that unless he was forced to do something he didn't want and was given an ultimatum. Do what "they" want or resign saying you had an affair. He took the latter. I'd like to know what the former was.
Story is that it was FBI which found out about it:
Petraeus resigns CIA, citing affair; FBI investigating
Kevin Johnson, Tom Vanden Brook, David Jackson, Jim Michaels and Aamer MadhaniShare
(Photo: T. Ortega Gaines AP)
3:48AM EST November 10. 2012 - WASHINGTON—CIA Director David Petraeus announced Friday afternoon that he has resigned from his post, acknowledging that he had shown "extremely poor judgement by engaging in an extramarital affair."
A federal law enforcement official said the relationship was discovered by the FBI during the course of an unrelated security investigation. Subsequently, a number of e-mails concerning the relationship were discovered, said the official who is not authorized to comment publicly on the matter.
The bulk of the e-mails were believed to be from Petraeus to Paula Broadwell, a writer and military analyst who wrote a glowing biography of the CIA director, the official said. Aspects of the FBI investigation were continuing, but the official declined to comment on possible targets of the inquiry.
In a letter to CIA personnel, Petraeus, 60, said he met with President Obama on Thursday and asked to resign because of personal reasons. Obama accepted his resignation Friday, Petraeus said.