The first verse is about the fear of giving up on a relationship.
The fear is so severe that sometimes they even want to forget they even care about the person.
The chorus highlights the reason why they try to remain faithful to the relationship - because they made a promise not to leave. 'A promise to the living end' could signify marriage or an eternal relationship.
The second verse is about the pain and fear which the person has experienced as part of the relationship though they are trying to make it new.
The last part of the song from 'I never meant to be a liar' is full of ambiguity as the listener is not sure whether the person has left or not. 'The shame is cutting into my skin' would indicate that they have left but the next line 'I'd rather die on my feet' sounds as if they are going to go down fighting for the relationship.