I've only seen this movie once, so my interpretation might be a little off, but it seemed to me to be an allegory of the price of fame, how famous people, in American popular culture in particular, are often driven to suicide. Of course there are a few holes in my theory: Julian never sought fame himself, but the relentless media attention (the group of children who followed him around), the riches and free stuff he received, and the boredom of a small town (representing America in general) has nothing better to do than make a celebrity out of an ordinary person. And finally, the callousness of the people when they drive him to suicide sums up the allegory.
Forgive my interpretation if it's wrong... but those were just my ideas.
Forgive my interpretation if it's wrong... but those were just my ideas.