People often only appreciate what they have when it's gone. Sounds like the impending roar of a jet engine is getting your attention.
It's good to plan but it's also good to live in the now. Have some more times together. Enjoy the time you have together.
Don't be worried or saddened about his eventual departure - be thankful for your friendship.
And remember: unless he's boarding a spacecraft headed to infinity and beyond, you too can hop a jet to his homeland one day.