It's about the end of a relationship, she still wants it
but he puts the blame on her, she leaves with her belongings (empty file cabinet meaning without blaming him, not having the "files") and taking her dog, while her pony carts it all and her away, but someday when he starts over, he'll realize and miss her, and will never fully be able to start over clean because he'll never forget her, and will realize he loves her now that she's gone
It's about the end of a relationship, she still wants it but he puts the blame on her, she leaves with her belongings (empty file cabinet meaning without blaming him, not having the "files") and taking her dog, while her pony carts it all and her away, but someday when he starts over, he'll realize and miss her, and will never fully be able to start over clean because he'll never forget her, and will realize he loves her now that she's gone