Like a House on Fire Lesson Plan

What does the idiom "like a house on fire" mean? How does the narrator of the story use this idiom to depict his relationship with his wife over the course of the story?

Like a house on fire means something that is very successful or that is going extremely well. When people get on like a house on fire, it means that they've become fast friends - in the same manner that a house rapidly goes up in flames. This is how the narrator describes his relationship with his wife, stating that well into married life they would even occasionally stay up late just talking. However, with his prolonged injury and the current state of his relationship, the narrator starts to...