he said sara left him after abydos, and in cold lazarus it seems obvious she hasn't seen him since abydos...i'm guessing divorced.
though the way they did interact in cold lazarus i'm thinking they're friends but that's all it's gonna be. she's the ex but it's an amicable situation.
face it, the way jack is, if he was still married he wouldn't be flirting with sam. in the military, adultry is almost as bad as treason.
frat rules aside, if he was married and someone thought they had a realtionship...it would be bad, very, very bad.