He used to date this girl, and had to leave for some reason. I think neither of them wanted him to leave, but he had to, or something. The girl promised him she'll wait for him endlessly, so they could continue where they ended after he was back. Then, after some time (probably several years?) he came back to their old home finding it empty, the girl left. She didn't wait for him endlessly as she was supposed to. But he keeps waiting for her, endlessly, wanting her to come back, even though he knows she won't come back.
OK, I might got it wrong, but that's what I understand it like.
Okay, here's how I take this song.
He used to date this girl, and had to leave for some reason. I think neither of them wanted him to leave, but he had to, or something. The girl promised him she'll wait for him endlessly, so they could continue where they ended after he was back. Then, after some time (probably several years?) he came back to their old home finding it empty, the girl left. She didn't wait for him endlessly as she was supposed to. But he keeps waiting for her, endlessly, wanting her to come back, even though he knows she won't come back.
OK, I might got it wrong, but that's what I understand it like.