I think the song is about Frenemies who used to be friends. I don't know if you've had this kind of relationship, but Frenemies are people who don't like each other, but pretend to for various reasons. Sometimes they have friends in common, so neither one wants to rock the boat by saying how much they hate each other. Sometimes, they use the other person as a punching bag to make themselves feel better. Like the person who says "Wow, you don't look as fat in those jeans as I thought you would" to make you feel bad and them feel better about their weight.
But in the song, these people had a real friendship at one point. The drugs seem to keep them together, or make it easier to tolerate each other. I think the line is "You want me to suffer just because you were born white". In England, being "Black" is a slang term for being depressed. Therefore, being white would be being happy. In "Back to Black", that was what she was saying. When her man leaves, her bright mood leaves and she goes back to her regular state of being black. That long segue was to say that, if Amy is generally black, which can be very draining for people to be around, and her friend is always white, they are going to clash. Perhaps her friend wants her to be more cheerful and she can't understand why Amy is so depressed. Amy feels like her friend shouldn't try to change her or shame her, but understand how she feels.
I think the song is about Frenemies who used to be friends. I don't know if you've had this kind of relationship, but Frenemies are people who don't like each other, but pretend to for various reasons. Sometimes they have friends in common, so neither one wants to rock the boat by saying how much they hate each other. Sometimes, they use the other person as a punching bag to make themselves feel better. Like the person who says "Wow, you don't look as fat in those jeans as I thought you would" to make you feel bad and them feel better about their weight.
But in the song, these people had a real friendship at one point. The drugs seem to keep them together, or make it easier to tolerate each other. I think the line is "You want me to suffer just because you were born white". In England, being "Black" is a slang term for being depressed. Therefore, being white would be being happy. In "Back to Black", that was what she was saying. When her man leaves, her bright mood leaves and she goes back to her regular state of being black. That long segue was to say that, if Amy is generally black, which can be very draining for people to be around, and her friend is always white, they are going to clash. Perhaps her friend wants her to be more cheerful and she can't understand why Amy is so depressed. Amy feels like her friend shouldn't try to change her or shame her, but understand how she feels.
Just my two cents.