Why did General Petraeas have to resign?

The official explanation that I have seen is that he could have been blackmailed into revealing state secrets. They can’t be serious.

Does anyone really think that he would have so wanted to avoid any embarrassment that he would have done such a thing? He was not an elected official. He had no constituency to answer to. His position did not require him to take a stand on social issues. Who the heck cares about his sex life?

If Bill Clinton had said, “Yes I had sex with that woman,” he would not have been impeached and he would still have been re-elected. Why do we apply a stronger standard to the CIA chief than the president?