“Her hubby is a good looking young doctor. I don’t get it.”
I guess you’re a man.
Unless her husband was cheating on her and this was revenge thing, Petraeus had nothing to offer her. Not good looks (husband handsome/Petraeus homely) , not money (husband a Doctor), not children (she already has them), not an elevation in social status (unless she wanted to be the queen of the Military Ball).
Sorry, still don't get it.