I think that the main theme of this song is about someone that is falling out of love with their partner and they are aware of it, like the lyric, "Lately, I've been slippin' away from you. Can you tell me, does it hurt today?" They are conscious of the lack of effort. And the other person knows it too, "I would do things and you'd get annoyed
I should've never done them, I wish I was different" They are trying to do whatever makes their partner happy in order for them to stay but they know that it's just not enough.