possibly it is yorke talking about how his girlfriend is either an alcoholic or drug addict in the first verse, the second has it seemingly waiting at hospital trying to stay awake with her and then the final verse has her already dead and him trying to cope with the pain that he is going through and he is starting to lose it himself and he is throughout the chorus just trying to figure out why it is happening to him and he can't find a rational reason for it so he blames it on a black star.
possibly it is yorke talking about how his girlfriend is either an alcoholic or drug addict in the first verse, the second has it seemingly waiting at hospital trying to stay awake with her and then the final verse has her already dead and him trying to cope with the pain that he is going through and he is starting to lose it himself and he is throughout the chorus just trying to figure out why it is happening to him and he can't find a rational reason for it so he blames it on a black star.