The person is hating themselves for cutting someone out of their life. They think that it may take time but that maybe they could start the relationship over again now that time has passed and things are different. Having someone you love or care about ignore you or cut you out is one of the worst feelings. In the song, it is obvious that not having the other in their life still has a significant impact on them and makes them feel as if they are the walking dead. This could be about a painful breakup or about any significant relationship one may have with a parent, great friend and so on...