The top-ranked interpretations are nonsense - the writers are confusing the video with the lyrics of the song. The lyrics are quite straight-forwardedly the musings of a young person (woman?) who has stepped away from a relationship, with feelings of deep regret, because her paramour/lover is falling into an alcohol-soaked, late-nights, and emotionally void, existence. The protagonist proclaims "It ain't me" who is going to help the boyfriend out the next time he is hung over and feeling wretched.
That's it.