I'm not a mother so I can't begin to understand how you feel, but I can imagine it's not much fun. But I can remember how it feels to have a parent missing you whilst you want to get on with all the exciting things that life is throwing at you. Young people can seem a bit selfish, rushing off here, there and everywhere, leaving mum & dad at home, wondering what they're upto. And what's the last thing they want to do, when they do finally show up? Sit down and talk about where they've been etc. I can hear myself now, giving my parents the sharp answer 'out!' when asked the innocent question 'where are you going?' , and I cringe! I was so selfish! But most kids are.
Best thing you can do is just what you are doing. Fill your diary with interesting productive stuff. Get out and meet some like minded people, so that when he comes back, you can cheery tell him all the interesting stuff you've been upto, rather than him feeling like you're lost without him.
He'll be so impressed that you're not some clingy mum hanging on his every word, and you'll have a terrific time!
Good luck : )