You will be much better off if you are both in the same service, most or all of them have programs where they ATTEMPT to assign spouses to the same geographic local. This will not guarantee that deployment schedules won't conflict of course.

If you just want to fly in the military, Marines and AF will both get the job done. If you want to be an airline or other commercial pilot someday the AF is the safer bet because you are essentially guaranteed fixed-wing aircraft if that's what you want. Marines probably have a 50/50 chance of helos.

But even AF fixed wing time won't help you...if the airplane is unmanned

Tough call. Actually I might suggest that you try the ANG/AF Reserves. That way you could dodge the helo/UAV bullet (at least initially), and you could follow your girlfriend around and commute to the reserve unit. You might need an airline job for travel benefits for the commute.

Safest way to protect your financial future from your ex-wife is to make sure she has/makes more money than you. Don't marry a hairdresser, flight-attendant, etc.