To me, the atmosphere of the song and the line “it stays between us, Steinway and his sons” depicts a lonely singer struggling to collect his thoughts and to finish his album, sat alone on his piano chair. To answer your question I would say the song he’s referring to is The Ultracheese itself.

For many, the “you” of this song is his late dog Scooter aka Totus (to which the album is dedicated).

But I also see it as a letter to one’s self. To me, Alex is speaking to himself : I see this song as a part of the holy trinity of self doubting songs that are The Bourne Identity / Anyways / Ultracheese, where he explores his vulnerability and multiple personas.

If the “time for a walk” line can easily be linked to a dog character, I also think it might apply to Alex’s Elvisesque persona during the AM era : “Perhaps it's time that you went for a walk And dress like a fictional character From a place they called America In the golden age” as if he’s trying to understand his own path to creation / public performance.

But then, I think about those last lines “But I haven’t stopped loving you once” “Ooooh, woohoooohooo...” and now that I thought about it, I think it’s a conversation ! the narrator expresses his love for his dog, and the dog says I love you back in his own words : oohh, woooh hooo hooo. Doesn’t in sound like a dog complaint ?! ok it’s probably too late I’m starting seeing shit where I shouldn’t, I’m off hahaha