I understand this song to be about a relationship what ended without a conclusion. Things between the first girl and the narrator slowly kind of fall apart, maybe there's no communication, maybe he cheated and she found out, but the line:
"Well, I would not have moved if I knew you were here"
illustrates that notion pretty clearly. He wouldn't have cheated or found a new partner if he knew what she wanted. now he realizes she still wanted to be with him and he can't get back to her and additionally, he's stuck with this other girl which is still good, but the first girl was always better.
I understand this song to be about a relationship what ended without a conclusion. Things between the first girl and the narrator slowly kind of fall apart, maybe there's no communication, maybe he cheated and she found out, but the line:
"Well, I would not have moved if I knew you were here"
illustrates that notion pretty clearly. He wouldn't have cheated or found a new partner if he knew what she wanted. now he realizes she still wanted to be with him and he can't get back to her and additionally, he's stuck with this other girl which is still good, but the first girl was always better.