Final answer:
The relationship with Catherine was uniquely profound and meaningful, distinct from superficial attractions or convenience that characterize other experiences.
Step-by-step explanation:
The narrator suggests that his relationship with Catherine was different from other experiences with women because it was not characterized by common attractions or superficial passions, but by a deeper, more profound connection. This distinction is drawn through various textual examples where relationships are portrayed either as unions of convenience, superficial attractions, or as genuine, deeply-felt bonds. The narration often provides insight into the characters' emotions and motivations behind their relationships, highlighting when a connection is unique or of significant depth compared to others.