Unlikely that he's active duty if he's been in charge of the CIA...
I don't have confirmation of this but there is some rumor going around the affair started when he was active duty, however.
Yeah. I saw a report (Catherine Herridge, as I recall) who said that too. That an extramarital affair on the part of an officer is "conduct unbecoming" and a serious offense. To the point that it's possible Petraeus could be pulled from retirement and court-martialed for it, then demoted and retired at a lower rank.
That sounded unlikely to me, but it was still listed as a possibility, because it is considered that bad an offense.