"He sees this as a failure, and this is a man who has never failed at anything," said an unnamed friend, quoted on CNN.
"It's going to take a long time" for him to move on from the scandal, retired army colonel Steve Boylan, a former spokesman for Petraeus, added in an interview with NBC's Today show.
Boylan, who said he spoke with Petraeus over the weekend, said the former general's wife of 38 years, Holly, is "furious". He also said Petraeus ended the affair four months ago.
Three days after the announcement that one of the biggest names in national security had stepped down from his post in disgrace, details of how the Petraeus affair became public are just beginning to emerge.
"This is about something else entirely, and the truth will come out," Paul Krantz, the father of Petraeus's mistress Paula Broadwell told the Daily News from his home in Bismarck, North Dakota. "There is a lot more that is going to come out … you wait and see. There's a lot more here than meets the eye."
The FBI began to investigate Petraeus after it received complaints about "harassing" anonymous emails Broadwell sent to Jill Kelley, a state department military liaison who was friends with the general. In the course of reading Broadwell's emails, the FBI found sexually explicit correspondence with Petraeus, the New York Times first reported.
The investigation of Petraeus began over the summer but was kept secret from Congress.
President Barack Obama reportedly found out Thursday morning – just one day before the affair was made public. Senate Intelligence Committee chairwoman Dianne Feinstein found out when she saw the headlines.
Feinstein has warned she will open a Senate investigation into the apparent delay in notification about an affair that "could have had an effect on national security".
"We should have been told," Feinstein said on Fox News Sunday.
The FBI investigation of Broadwell determined there was no threat to national security.
The first elected official to know of the affair appears to have been Washington state congressman Dave Reichert, who brought the matter to the attention of House majority leader Eric Cantor.
"Our office stands by the accuracy of the New York Times article as it pertains to Rep Reichert," a spokeswoman said in a statement. "We have no further comment about our involvement."
Petraeus was scheduled to appear at a closed Senate hearing this week on the fatal attack on the US consulate in Benghazi, Libya.
Critics of the president sought to make the administration's early statements about the attack, which inaccurately described a spontaneous protest, an issue in the final weeks of the presidential campaign.
That criticism has now expanded to allegations that Broadwell, who got to know Petraeus while writing his biography, was privy to classified information about the Benghazi attack.
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