The relationship between the two has always been like that of a sword and its scabbard.

This couplet beautifully describes a relationship that's incredibly close and intertwined, just like a sword and its sheath. They are inseparable; one protects and holds the other, and together they form a complete unit. Imagine how perfectly a sword fits into its sheath, becoming one. It suggests a bond where each person is essential to the other, perhaps even dependent, and they move through life together, always complementing each other. Their connection is deep, harmonious, and enduring.