This guy feels that his relationship is doomed (whether it true or just insecurity we can't be sure)...he knows that soon she will realize that he is no good for her and they will be break up. He will be the enemy, held at a distance. Her optimism (the glass half filled) will be diminished (spilled).
In the chorus he mentions the things he's done wrong (forgetting things like her birthday perhaps, all their fights) and offers some hope that maybe he'll be forgiven for those things, maybe they will be forgotten, maybe they can continue in their relationship and sharing everything - but that hope quickly fades ("but maybe not")
This guy feels that his relationship is doomed (whether it true or just insecurity we can't be sure)...he knows that soon she will realize that he is no good for her and they will be break up. He will be the enemy, held at a distance. Her optimism (the glass half filled) will be diminished (spilled).
In the chorus he mentions the things he's done wrong (forgetting things like her birthday perhaps, all their fights) and offers some hope that maybe he'll be forgiven for those things, maybe they will be forgotten, maybe they can continue in their relationship and sharing everything - but that hope quickly fades ("but maybe not")