The speaker is looking back on a relationship that has ended, or at least changed beyond repair, yet the love hasn't faded. Closeness to this person makes the speaker's body "forget" old regrets, as if touch can quiet what the mind and even the liver, an odd, physical image, have been storing up.
The center of the poem is a memory: the two of them waiting for a plane, listening to a cover song under a "muted sun," then singing together, feeling free. The speaker calls it the most beautiful moment they shared. But that memory now hurts. The song can't be listened to anymore, which suggests how closely joy and loss are tied together.
The ending is quiet and steady. Despite the pain, the speaker will "always adore" this person. The phrase "final summer / of our happiness" gives the poem a tender, wistful mood, with sadness sitting right beside gratitude.