Sort of my Black family, mostly Bellatrix, head cannon as to why they're so screwed up. Amazing quote taken from Stigma, (.net/s/6428576/1/Stigma) a Harry Potter fanfiction.
"Insanity and incest run hand-in-hand in most pure-blood families."
Old money and old ideals keep the cycle alive.
When they were little their father would take Bellatrix off into his private quarters, and her mother would just look the other way. Bellatrix being the eldest was the most logical choice. Narcissa was always jellaous of the attention, even though Bella told her not to be. Thus began the slow destruction of Bellatrix Black.
But it didn't stop there Bella tried to continued the cycle with Andie, but she not much younger than Bella would have no part in it. She always was the passivly rebellious one, much like the muggle hippies of the sixties. But Narcissa being much younger and impressionable succumbed quite effortlessly. I mean it wasn't hard when she thought the world of Bellatrix and trusted her implictly.
Narcissa lost in the dulsion grew to love Bella and thought of their realtionship as almost perhaps normal. However their perverse love pushed Andie farther and farther away. It was always Bella and Cissy and there was no room for her, not metion the how Bellatrix despised her after her rejection. Narcissa didn't understand and tried to stay friends with both of them, but Andie was too differnt and she was just to brainwashed by Bellatrix. When Andie left to runoff with the mudblood, happy to be rid of her Bella replied "Good ridance," and told Cissy that they didn't need her, and it would always be them two.
Narcissa loved Bella and Bella just left her to run off with Him. She left just like Andie. So Narcissa did the thing that would make Bella most angry; she married her neminsis, Lucius Malfoy. Narcissa didn't pratically like him, but he was enamored with her, and if Bella ever came back she'd be furious. Eventatully Narcissa did grow to love Lucius. But Lucius had to work very hard to get Narcissa, granted the only reason it ended up working was his long blond hair, which reminded her of herself, she really was quite the narcissist when it came down to it. And she became very happy with their maggiage and even happier as a mother.
Bellatrix was a whore, because voldemort didn't want her. He didn't even need her. He was much too unhuman for such carnal urges. So bella trying to fill the void left by his rejection, slept with everyone. But it never quite helped, not to say for lack of trying or even lack of determination, for all of that she had. She could have had everyone, everyone but the one she really wanted. The man she wished for, who she'd do anything to please. She would always pretend. With her eyes closed it was almost a fictional heaven. Rodophus was boring, with Lucius it was forbidden, with Severus it was hate, but with Him it was non existant, but even the best still did nothing for her, she felt nothing, for it wasn't him inside her. However, it didn't stop there; pleasure was nothing, pain was nothing. Her love for him distroyed her. The desensitivy to feelings led to a loss of emotions and thus a loss of conscience. All the love she once had simply replaced with dark obsession. She once was, dare to say, almost normal, sane even, but that was long gone, even before her stay in Azakaban.
In retrospect there was no way she could have ended up any other way.