Keep in mind that there aren't really any rules here. The two of you are already outside the norm with your unusual geographical pairing and whirlwind romance. But beyond that, there's nothing about your future together that's any more or less secure than anyone else's new relationship.
At this point, it's just about managing your expectations. Instead of worrying about the future, take the situation day by day.
Pay close attention to your feelings. If the sadness you feel being apart starts to outweigh the happiness of speaking and occasionally visiting each other, reassess. Do what makes YOU happy.