The movie is about Tom growing up.

He built up a whole romantic fantasy that wasn't real. Summer genuinely likes Tom, that's why she's nice to him, even at the end. But she makes it crystal clear that she did not want a serious relationship with him. He chooses to ignore that. He thinks they are 1 record away from being a perfect match.

Summer is the best thing that ever happened to Tom. He learned that he needs to feel satisfaction and pride in himself instead of trying to find it in a woman. Then he's emotionally mature enough when he does meet a perfect match.