Another hint that Paul may have been thinking about his rift with the other Beatles, and particularly John, when he wrote the song, can be found in the second verse, which begins: "Well I thought you was my friend." The couplet that follows was altered between the time Paul wrote it and the session. In Paul's handwritten manuscript (which he titled 'A Dog Is Here'), it is "But you left me down / With a heart that never mend." The crossed-out final line is replaced with "Sent my heart around the bend," transforming its subject from heartbreak to madness. At the session, he changed "left me down" to the more straightforward "let me down," more precisely echoing John's 'Don't Let Me Down.'
The McCartney Legacy: Volume One, Allan Kozinn and Adrian Sinclair (2022)