I'm pretty sure this song is about the feelings of someone whose lover left them. He may be alive and breathing, but he feels dead inside, drained of all hope and strength from losing the one he loved. He doesn't want to accept the fact that it's over, and he can't just forget about it, but he still realizes, painfully, that it's over, that he can't change that, and that he has to live with that fact.
I'm pretty sure this song is about the feelings of someone whose lover left them. He may be alive and breathing, but he feels dead inside, drained of all hope and strength from losing the one he loved. He doesn't want to accept the fact that it's over, and he can't just forget about it, but he still realizes, painfully, that it's over, that he can't change that, and that he has to live with that fact.