There isn't really any other way to put this, so I'll just say it bluntly: You miss your best friend. He's always been there for you when you needed it but didn't necessarily want it. And for the second, maybe third, time in your life you are miles and miles away from him.
It isn't that you miss his physical presence, you never really have. And if you were back home, you'd still be two hours away from him, it is that he isn't as easily accessible as he used to be. After spending close to a decade with him, you don't really know what life is like without him. He has always been the one healthy relationship you've had in your life.
But even now, when you're the farthest away from him that you've ever been. You can still hear his voice in your head. He's telling you to live your life for once and to not worry about him or your family or any of your other friends. He says to drink double the amount you're used to because he can't be next to you drinking. He laughs through an old joke that makes the both of you laugh so hard you keel over and chuckle into a loud cry on the floor. He's with you. He's saying we all have our own personal Everest's to climb and he knows that you can do this on your own.
You, on the other hand, are playing a song the two of you listened to a couple of weeks after you first met. He had only really listened to hardcore and you had only really listened to pop punk. And for the first time in what felt like forever you decided to share a piece of your life with someone else because you had this aching feeling inside that he would understand the lyrics as much as you did:
"So hell can have our fucking names because we'll fail and fuck up until we're in the grave. So I'll search for someplace where we wont die alone someday. You know I need to back up from these dead ends. So back me up my friend."
And little did he know at the time -- years ago -- that he would back you up the same way the song pleads for a friend to back it up. And you have done the same for him. And there's something about knowing that you are there for someone else that makes you feel at ease. So right now, while you're laying in bed reminiscing about all the old times, the good times, a part of you feels that he is doing the same thing.
You miss him. You always will. Even if he lived down the block, you would still miss him the same way you do now. But you know that you won't miss him to the point where it incapacitates you. You'll remember his voice, his words, and his music. You'll listen to it all and wait for the next time you'll get to see him.