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And Bellatrix, was, as I think is clear— you know, I doubt that people will be particularly shocked to hear, ‘cause I’m sure they’ve deduced, that Bellatrix is madly, romantically in love with Voldemort. This is— you know, that’s the obsession of her life. And I believe that Helena Bonham Carter had to be asked to tone it down after she— (laughs) The producer called me and said, you know, give me some background on Bellatrix so we can tell Helena about it. And I said, well of course, it’s a sexual attraction. She’s madly in love with this man, and obsessed with him. (laughs) http://www.accio-quote.org/articles/2007/1224-pottercast-anelli.html

Question: Did Bellatrix ever love her husband, or did she have love only for Voldemort
J.K. Rowling: She took a pureblood husband, because that was what was expected of her, but her true love was always Voldemort.
http://www.the-leaky-cauldron.org/2007/07/30/j-k-rowling-web-chat-transcript/