Resignations don't generally follow. Newt Gingrich survived sex and ethics scandals. He resigned as House Speaker after the Republicans faired poorly in 1998 off-year elections.
In 1999, extramarital sex defrocked Speaker-elect Bob Livingstone. He could have stayed, but opted to become a high-paid DC lobbyist.
Extramarital affairs didn't defrock past notable officials. They included Alexander Hamilton, Thomas Jefferson, James Buchanan, Grover Cleveland, Warren Harding, Franklin Roosevelt, Dwight Eisenhower (during WW II), Jack Kennedy, Lyndon Johnson, and Bill Clinton. Unconfirmed rumors also surfaced about GHW and GW Bush.
Jimmy Carter once admitted to having "lusted in his heart," but never let it go further than that.
As more information and rumors surface, expect lots more written about Petraeus. Another emperor has no clothes. Petraeus was more paper hero than real one.
The man behind the image was fake. He's a shadow of how he and spin doctors portrayed him publicly.
Competence didn't earn him four stars. Former peers accused him of brown-nosing his way to the top. It made him a brand as much as general. Talk about him being presidential material surfaced.
In 2007, Time magazine made him runner-up as Person of the Year. The designation is as meaningless and unworthy as Nobel Peace awards.