In just three lines, the speaker compares their memories to a song, and not a complete one. The memories are only "bits and pieces," fragments that don't quite add up to the whole tune. Then the last line lands: "you're always the chorus." The chorus is the part of a song that keeps coming back, the part you hum without trying. So whoever "you" is, they return again and again, no matter which other memories surface.
The speaker seems to feel a mix of fondness and helplessness. There's warmth in the image of a song, but "always" suggests this person can't be shaken off, and the poem doesn't say whether that's a comfort or an ache. Judging by the title, "#SIX," this may be one piece in a numbered series, though the poem alone doesn't tell us more. The mood is quiet, wistful and intimate, like catching a familiar melody and realizing exactly who it reminds you of.