She's 16, she most likely doesn't have the maturity yet to deal with it. I mean, think about it. You're telling a 16 year old girl that her boyfriend wants to leave her for a long period of time, see her much less often, and have a higher risk of casualty. What's the expected reaction? Even if she was outwardly happy for you she would still take a while to soak it all in.
There's a big difference between a college guy (even in distance as you are) who can visit over the summer/breaks/whenever and a military guy who only gets leave so often and must sometimes pick between family and girlfriend.
There's a big difference between a college guy (even in distance as you are) who can visit over the summer/breaks/whenever and a military guy who only gets leave so often and must sometimes pick between family and girlfriend.