In the grand scheme of things, joining the military (especially as an officer/pilot) is going to be a life-changing experience, perhaps a life-defining experience, and is going to be a major factor in your life for 10 or 20+ years.

Relative to that, a 6-month girlfriend is pretty insignificant unless you know for SURE that she is the ONE. Sounds like that's not the case, so I would make your own decisions on the military and then cut her loose if needed.

You are right, military is a LOT easier with a supportive spouse...or no spouse. Entry-level military and/or aviation is probably going to be more fun and less stressful if you single.