Is your girlfriend concerned about being a military wife, or being a fighter pilot's wife?  If it's the military life she is concerned about, there are several books and forums that are by military wives on what to expect and how to deal with separations.  If it's the life of a fighter pilot's wife she's concerned with, that's something else altogether.

As far as being gone, fighter pilots are not deployed any more than virtually any other airframe or non-flying AFSC.  In fact, in some cases fighter pilots are gone less.  I am a fighter pilot, and I have a wife and kids.  I have not spent nearly as much time gone as I thought I would.  Yes, you will be gone, but that is true no matter what job you end up in the Air Force (with a few exceptions).  The current trend for fighter pilots is approximately 4 months gone for every 1.5 to 2 years home for "combat" (ie, a tour in Iraq), with a few other training deployments interspersed in there.  The forecast is not nearly as gloomy as some would have you think.  Besides, you could be in the Army...

I have some information on the family life of a fighter pilot on my website at www.ChristianFighterPilot.com.  Feel free to email me at cfp@christianfighterpilot.com as well if you have any questions.  I don't check this board terribly often, but I'll try to check to see if you reply.