I totally know how you feel. My boyfriend is a marine and it is a pain in the butt.
He however is a reserve so that helps out alot. He's not gone constantly.
Anyway, I just try to keep myself busy... constantly. I will hang out with friends, study schoolwork(for once), or pick up a new hobby(when he was gone for SOI I learned to crochet!). Anyway... I know it's hard, and it seems like it takes forever, but like they say, time flies when you are having fun. So find some things to do and get out and do them! Before you know it he'll be back in your arms again.