Irrelevant to the charge of adultery. If there are additional charges such as violations of operational security, and they are criminal, then they will be pursued separately. The adultery charge would stand or fall on its own.
That's not to say Petraeus didn't divulge classified info, nor even that he didn't do it as a result of an illicit affair, but those charges will still be separate. An affair can be part of the proof presented that explains how Broadwell came into possession of classified info, but I'm thinking that will require a lesser threshhold of proof than proving actual, penetrative adultery.
Anyone else remember the kenyan taking an extra day off from campaigning a couple weeks ago? Seemed odd at the time. Maybe that day off was related to this?