The speaker looks back on a past love and admits something unsettling: the feelings were real, but the reasons are gone. Pictures, messages, songs and late-night poems all remain as evidence, yet their meaning has drained away. The repeated "didn't i?" and "didn't you?" sound like someone testing their own memory, half asking for confirmation that it all really happened.
The long list of "what those things meant" builds a sense of emptiness, as if the speaker keeps reaching for details and coming up with nothing. Then comes a twist. The speaker hopes the other person has forgotten the books, the songs, the nights on the grass, even the love itself, but not the speaker. That wish is a little contradictory, and that is the point. Letting go and wanting to be remembered pull against each other. The mood is wistful and tender, with a quiet ache underneath, and it ends on the speaker's own memory of the person, which is the one thing that hasn't faded.