The speaker begins with a string of questions about a close friendship. What brought these people together? Was it shared tastes, mutual respect, or simply feeling at ease? The poem keeps testing answers and then setting them aside. Music, mountains and a love of talking about life matter, but they aren't enough. Something clicked when the friends first met, like a seed that grew over time.
Midway through, the poem turns to memory: bike rides, hill walks, rain, cold, warm drinks, forests and cities. These quick images make the friendship feel lived-in and physical. The speaker admits the time together felt too short.
By the end, the questioning softens into gratitude. Each friend filled a gap in the speaker and also carried a piece of him. Even if they part, they have "filled each other's cup." The closing comparison to books kept close at hand gives the title its meaning. The mood is warm, reflective and quietly thankful.