How do I cope with my older but close friend going over to Iraqi?

I used to live on a military base and usually there were older kids for me to hang out with. When I was 10 I made friends with a 15-year-old boy. He became a part of my family (to me emotionally). We have been best friends ever since. He joined the USMC not long ago and this weekend he's going over to Iraqi. I'm so scared for him. I know he's strong because he's protected me if guys try to mess with me, but he's barely an adult! How am I going to cope with this? I already miss him so much.