She was what Voldemort would have been if he had been raised in a loving, privileged family. She was what Voldemort wanted to be for she was loved, Pureblood, and an aristocrat as well. He probably saw that and her potential and decided to take her under his wing, to make her his.
He did not love anyone, and did not care to be loved. He felt nothing for his family, and only wanted his friends in school to rally around him because he wanted to hold power over them. Bellatrix Lestrange was obviously in love with him and worshiped him, but he only cared for her servitude, not her.
Bellatrix, herself a case study in the Dark Tetrad personality traits (narcissism, Machiavellianism, psychopathy and sadism), is drawn to those traits in Voldemort. She sees Voldemort as the only person worthy of her devotion. He is the only one who surpasses her in power, cruelty and ruthlessness.
The most speculated reason why Voldemort wanted a child is that he needed a backup relative to help him create a new body. Voldemort is immortal, but it would only take a stray curse to destroy his body and send him back to the pathetic state he was living in before the events of Philosopher's Stone.
His reaction to Bella's death was akin to his reaction at the loss of the Cup, which was when he realised that his own immortality was jeopardised amidst war and his own death could have been near.
Why doesn t Harry use Avada Kedavra on Bellatrix? Harry didn't use that spell because he cannot bring himself to kill anyone. He is not a killer.
The author explicitly states that both women were fighting to kill, despite Molly refraining from casting the Unforgivable curse Avada Kedavra. The result of the duel actually comes about as a result of nothing more than spectacular accuracy on Weasley's part.
Bellatrix Lestrange Killed her own cousin, Sirius Black: She killed Sirius (who was her cousin) during the battle at the Department of Mysteries. She was remorseless and was cackling in glee after she had murdered Sirius.
As much as Bellatrix loves Lord Voldemort, she equally hates Harry Potter, considering him the greatest threat to Voldemort and his plans. She will do anything to assist the Dark Lord's desire to defeat Harry.
Voldemort's reaction towards Bellatrix's death proves that the Dark Lord acknowledged her as his most dedicated follower. The Dark Lord immediately tries to kill Molly Weasley in vengeance before Harry intervenes. Bellatrix was loyal until her death, and was undeniably Voldemort's best and last lieutenant.
Bellatrix used a powerful "love potion" on Voldemort and they have sex while he is temporarily obsessed with her. She then uses obliviate on him while he sleeps (you know, he falls asleep after his post-sex cigarette) and tells everyone that the baby is her and her husband's.
The 'boy who lived' aka Harry Potter, aka Daniel Radcliffe had a crush on Helena Bonham Carter, who starred as Death Eater Bellatrix Lestrange in the film. During the reunion, Daniel revealed that he had a crush on her and even wrote a letter to her.
Delphini "Delphi" Diggory is Voldemort's secret daughter (wow, the Potterverse is turning into a soap opera). She wants to resurrect the Dark Lord—not necessarily to bring evil to the world, but just because she wants to meet her dear ol' dad. It's actually kind of sweet…in a completely evil way.
Bellatrix had a fear of rejection as well where Voldemort was concerned, wanting nothing more than to please him but was always frightened that she would lose his favor.
With all of those symptoms being met, it wouldn't be unreasonable to consider her as having a borderline personality disorder. Bellatrix Lestrange “was obsessively in love with Lord Voldemort, which extended to her being… attracted to him” (wiki).
Bellatrix had a fanatic obsession with the Dark Lord although she was clearly fearful of his magical abilities and absolute power over his forces. She's almost as sadistic and homicidal as Lord Voldemort, with a psychotic personality.
Harry himself is a half-blood, since his pure-blood father, James, married a Muggle-born witch named Lily, and his maternal grandparents were Muggles.
Cruciatus Curse ('Crucio')
Harry tried to use this spell himself. The first time was against Bellatrix after she had killed Sirius.
After being on the run from a bunch of Snatchers, the gang were taken to Malfoy Manor, where Bellatrix proceeded to torture Hermione using the Cruciatus Curse. It was a testament to Hermione's toughness that she was able to walk away without lasting damage.
Voldemort's attempts to trick Harry into killing Bellatrix would have done far more harm than good to his sinister cause, as Harry killing Bellatrix might have resulted in dire consequences for him, but he'd remain one of Voldemort's greatest threats and the Dark Wizard would be missing his most trusted lieutenant.
He endured horrible things right from his unpleasant childhood, the death of his best friends to spending twelve years in Azkaban. His tragedy however didn't stop at his framing and imprisonment. Sirius met an undeserving death at the hands of Bellatrix Lestrange during the Battle of the Department of Mysteries.
Her evil nature was a direct result of her love for the most vicious wizard in the history of the Wizarding World. Bellatrix was a powerful wizard. She was trained by the Dark Lord himself. Therefore, she had exposure to all things evil and she delved into it wholeheartedly to please her Lord.
Though Harry encountered many opportunities that deemed Avada Kedavra necessary, it remains as one of the Unforgivable Curses Harry Potter never cast. For one, he viewed the spell as an immoral practice commonly used by users of the Dark Arts.