He and Bella bonded over it. The fact they were never the favorite, always a last minute thought and never a priority.
His parents like Regulus better. That was a fact. It was evident everyday, in a thousand different ways. How they always spoke kindly to Regulus, in a tone of voice he'd never heard directed to him. How he'd never seen them lay a hand in Regulus, but he'd felt the sting much more than he'd wanted. It made him so mad, why were they so kind to Regulus? Was he not just as strong? Just as brave? Just as powerful? What made Regulus so much better than him? In the end he just scowled, scowled that special scowled that he only gave to his parents. The one that just made them slap him thrice more times than previously before telling him to "erase that look from his face immediately." He never did.
"I know how you feel," a voice came from behind him. He whirled around, tearing his eyes off of the sight of his brother being praised. He glared when he saw who it was.
"I don't want your sympathy," He growled glaring at the curly haired girl.
"But you do. You want to know that you aren't the only one that feels this way. I can tell you one thing for sure, you aren't the only one," Bella replied, a sad edge to her voice.
"Then how do I feel miss know-it-all?" He snarked, staring glumly down at the scene before him.
"You feel mad, yet confused because your reason for madness makes no sense at all. You have so many questions, but you can't ask because you know what will happen if you do. The only person you can ask hasn't got a clue of what's going on. So your left, in the dark, just as mad as you were before." and with that, Bella put a hand on his shoulder, gave him a small, reassuring smile, and left.
He should've realized it sooner. He saw that same scowl on Bella's face, he'd seen the bruises and the cuts, he'd seen it all. It must've been the fact of how Bella told the most convincing lies, carried herself with the perfect air of self-confidence, that nobody even thought to suspect. Perhaps it was a bad thing, the lies she told. Nobody could help her now. she was stuck, stuck in her own trap of lies, forever doomed to suffer from her words of reassurance. He'd seen the same look on Bella's face.
They'd bonded over it. Not being the favorite. A small smile here, an encouraging word there, to remind each other that they weren't alone in this world, that somebody cared. They helped each other get over the neglect of their childhood, and to strive to be bigger and better than their parents' wildest dreams. To prove that they weren't unworthy of their parents' praise. That they should be prefered child, and not Narcissa or Regulus.
They always said it was his fault. That he ruined the family name. He laughed. Little did they know, it was really their. He wouldn't have turned away from their oh so precious traditions. Not if they hadn't made him feel scorn at them, not if they hadn't made him despise the very roots that they came from. The reason he'd turned, turned away from the Black family and the Black magic, was because they made him despise everything that had to do with the no good, blood sucking leeches that had no right to call themselves his parents. No, it wasn't his fault, it was theirs. And he was absolutely fine with it. The only thing he regretted, was losing his Bella.
So in the end, only Sirius escaped. Only he escaped from the world that watched his every move and scorned every wrong action. He escaped from the world that the only thing that mattered was who your parents' preference. Would they support you, or would they leave you to die? Only Sirius escaped, and Bella was doomed from the beginning by her reassuring lies.