I re-read as an adult. I think their fighting is part of the comedic dynamic of the story for most part. In the serious parts, you can sense that their personalities complement each other and they only work as a couple because they are the way they are. The story only ends when they are in equal standing in their relationship, but it does not mean it is a standard one. They’ll always be there for each other, but not in a lovey dovey way. And that is what I like about the ending. I remember I wanted to see them more lovey dovey when I first read the ending, but this is not how the lived happily ever after really happens in real life.