The only sort of behavior in the military that should be counted as unprofessional is something that renders a person unfit for duty. If a soldier wants to go out and join an orgy, get drunk and stoned, and howl at the moon while dancing naked around a bonfire, it's all irrelevant so long as he shows up for duty bright and alert and energetic.
If Petraeus had been in any post but the CIA, this would have been no big deal. So I think he should just lay low till the midterms, then Obama can make him SecDef.