Draco's despicable actions were carried out in The Half-Blood Prince through fear of Voldemort and a misguided thought that he had no other choice. His scheming and experimenting eventually led to him syncing a Vanishing Cabinet to one in Borgin & Burkes.
What was Draco supposed to do in Half-Blood Prince?
Draco planned to repair a Vanishing Cabinet that Peeves had destroyed four years previously, in order to smuggle Death Eaters into Hogwarts to assist him in killing Dumbledore.
When Draco attempted to utilise the Cruciatus Curse, Harry retaliated with Sectumsempra, a spell he remembered having read about in the Half-Blood Prince's copy of Advanced Potion-Making, which caused deep slashes across Draco, heavily wounding him and causing him to fall to the waterlogged floor, his blood floating ...
With this, Draco's arc throughout Half-Blood Prince and Deathly Hallows could be seen through a much different light. Draco's visibly sickly appearance is because of his lycanthropy, not due to the amount of stress he's under to complete the nearly impossible task of murdering Dumbledore.
His tears were due to the fact that since the bird had died, he had failed once more to repair the Vanishing Cabinets. Draco needed to repair them in order to give the Death Eaters a safe way to infiltrate Hogwarts. Failure meant death, Voldemort had made that very clear.
It's implied that Septum Sempra is Snape's own creation, that he used a specific counter-curse to heal Draco, and that the spell isn't designed to be instantly fatal, but to inflict a gruesome, but relatively slow death if left untreated. It's likely Snape is the only person who knows said counter-curse.
Sectumsempra was a curse invented by Severus Snape that lacerated the target and caused severe haemorrhaging. Snape created it as a student of Hogwarts, with the intention of using it against his enemies, likely including the Marauders, with it becoming one of his specialities.
She married Rodolphus Lestrange after leaving Hogwarts "because it was expected of her" to marry a pure-blood. However, Rowling stated in an interview that Bellatrix truly loved Voldemort.
The injury was caused by Snape's Sectumsempra spell in order to stop the Death Eaters from hurting George (who he thought was Harry) and Lupin, but missed and hit George. Hermione and Kingsley then arrived, both unharmed, followed by Arthur and Fred Weasley, both concerned for George.
But in Harry's narration, where he was paying attention to the smallest steps Draco took, there was never a sexist behavior of him towards any girl. During the whole saga he was never close to any girl other than Pansy, and it was never confirmed whether they dated or not.
Draco Malfoy never had that many close people, and when he married Astoria and they had their son Scorpius, it looked like things would finally get better for him. But Astoria died and Draco had to raise his son as a single dad - and considering how Scorpius turned out, he did a good job.
He's, like, a side character that you wouldn't expect to be attractive, which makes him even more attractive. He just gives off a different vibe than other characters who are supposed to be evidently good looking. Also, the fact that he was broken and tried to be a good person also makes him even more attractive.
Malfoy spots Harry and casts a Cruciatus curse; Harry, defending himself, using the Half-Blood Prince's Sectumsempra spell without knowing its effects. To his horror, it gashes Draco's face and chest, spilling his blood everywhere. Moaning Myrtle flies off, screaming.
By Harry Potter and the Deathly Hallows, it's a stretch to call Draco a villain anymore. We just watched — or read — him struggle to reconcile his choices and morals in The Half-Blood Prince. He can no longer justify his actions, and is far more aware of the evil he was born and raised into.
Vulnera Sanentur was the song-like incantation of a healing spell which was used to heal deep wounds, which could also be used as the counter-curse for the curse Sectumsempra.
In the final movie, Harry Potter and the Deathly Hallows pt. 2, Molly first hits Bella with a spell that freezes her, most likely Petrificus Totalus. Then, she launches another one that shatters her entire body into pieces, which could be expelliarmus, bombarda, stupefy, or any spell that can produce such an effect.
There is likely a good reason that the Sectumsempra is not an unforgivable curse. It's mostly because Sectumsempra is Snape's personal curse that he created. It is not a widely known or used spell, and it is one that he kept secret — which means it can't be added to the list since no one really knows about it.
Harry Potter had a few love interests during his time at Hogwarts. Though he eventually settled down with Ginny Weasley, he also had a thing for Cho Chang in his earlier school years. Then, of course, there's his secret love for Draco Malfoy…
He didn't want to make Harry uncomfortable; after all, they live together, eat together, work together and even share ownership of a temperamental cat. Harry just laughs, “I'm in love with you too, you git.” Draco kisses him, putting years worth of pent-up longing into one moment.
It's safe to assume that Draco's hatred of Harry was fueled by jealousy. Although Draco attempted to disguise his jealousy with confidence, it still makes an appearance throughout the franchise. Harry is an incredibly talented wizard – something which Draco greatly admired.
Sectumsempra is a curse invented by Professor Severus Snape, during his childhood, when he was known as "The Half-Blood Prince". He created it with the intention of using it against his enemies, and it soon became one of his specialties.
J. K. Rowling stated that the pain from Harry's scar on his forehead was caused by the piece of Voldemort's soul trying to leave his body through the wound it entered to rejoin its master's soul.
He promised to protect Draco Malfoy from harm and guide him whilst he attempted to perform the task the Dark Lord had asked him to do: to kill Albus Dumbledore. Snape was actually a double agent working for Dumbledore, who requested Snape to kill him anyway to spare him of a painful and humiliating death.
