personally, i see this song as him saying "I know what we have is over, but i cant get over you" its more of a saying goodbye, but he knows he still longs for it, "'Cause a part of me is dead and in the ground, This love is killing me, but you're the only one" hes saying how a part of him that loved this person is in the ground as he knows its over, but this person is the only one he loved.
personally, i see this song as him saying "I know what we have is over, but i cant get over you" its more of a saying goodbye, but he knows he still longs for it, "'Cause a part of me is dead and in the ground, This love is killing me, but you're the only one" hes saying how a part of him that loved this person is in the ground as he knows its over, but this person is the only one he loved.