Joining The Army.

Im planning on joining the army, im only 16 at the moment but my recruiter says that when i turn 17 in february i can join the Army Reserves. I would then go to basic training this comming summer, and then come back and finish my senior year of high school. The problem is, i have a girlfriend which whom i have been with for over 2 years now. I told her i plan to join the service when i graduate, but she doesnt know i have talked with a recruiter and am leaving this summer for basic, any advice on how to tell her the news and if anybody is in the service, tips would be helpful on staying together with a loved one, thanks.