You seem quite dependent on him. WHY are you missing him so much? Is it because you miss the way he makes you feel? Miss the company? Miss the sex? Or is it because you feel better when he is close to you so you know what he is always up to? Are you scared he isn't going to miss you as much and realise he likes being on his own?
You did mention you feel jealous. I think this is perhaps what is really behind the anxiety. Plus general insecurity. It is normal to miss our partners when they are away but if only one week is causing you anxiety like this then you need to examine why. Just stay busy, throw yourself into your exam prep and he will be back before you know it. It is healthy to have time apart. Think of all the great sex you'll have and all you can talk about when he is back. Plus, it is a good measure of how healthy your relationship is. If you both missed each other like crazy then you got nothing to worry about.
When he is away for longer isn't there ways you can keep in touch ie Skype, sms, calls etc?
Some people are drains and some are radiators... Keep clear of the drains and hug the radiators!