Are you going to see him at all during those 4 months? Any visits in between? That would help, I think...
As for feeling numb, yeah, that happened to me sometimes. Along with every other emotion I could possibly feel.
Sometimes it was the only way to cope with the situation... because if you allow yourself to miss someone that much... well, you kind of stop being able to function in your own life, which isn't good. You have to come up with a way to cope, to make each day pass, which puts you closer to being reunited with him.
For ktspktsp and I, we usually talked briefly on the phone at least once a day, but otherwise it was best to just be on MSN and be able to talk as if he was in the same room. Or, if we had total lack of communication (when I was in Africa for 2 months), we wrote letters to each other every day and collected them for later... and that was actually great. Strange, it was somewhat easier to be *totally* disconnected from him, than to have phone calls and e-mails every day to remind me of how far apart we are. So I'd say you should find the right balance of communication that will help you feel better, not worse.
Of course I am talking out of my ass about a lot of this. Every LDR sucks... everyone has their own way of dealing with it. How is James coping?