Hey there Sue, I totally know how you feel, because my boy is in the ARMY. He's currently in the field for two weeks(stationed in CO, I'm in AZ) and this is the first time in over a year I haven't been able to talk to him every day or two. Though on the upside for me, he snuck away last night and called me. It had been 7 days!
In any event, my best way of feeling not so depressed about not seeing/able to talk to him is to be really busy. I've thrown my self head first into getting into shape again and go to the gym 5-6 nights a week. I spend more time out at the barn with my horses, and spend way more time studying for school (which I know I should be doing anyhow!).
I think you two need to have the discussion as to what you are! If it's killing you it must be killing him! Have a talk with him about it, to finalize what you are to each other. I think that'll bring you a peice of mind. If you love him and you feel right about saying it, say it. It'll be emotional to admit how you feel, but it's way better than being dragged through the mud by not letting him know how you feel and knowing for sure (in his words) how he feels.
Good luck!