All Regulus Black ever wanted was to be loved.
Of course, the noble and most ancient House of Black was the farthest thing from a house full of love as you could get. In it lived a broken family - two sons and two parents - one son a 'disgrace and a shame', or as so he was told, the other son 'their perfect Slytherin who was nothing like his brother' or so they thought, and the two parents - uncaring about their sons happiness and well beings, and more concerned as to who was living up to the Black name.
Regulus Black was the younger brother - he was the perfect Slytherin of whom the parents - Wallburga and Orion Black - adored because he was nothing, nothing, like his rebellious older brother, who associated himself with mudbloods, blood traitors, and filthy half breeds. Regulus thought his older brother a fool for a long time - did he not know how disgusting his company was? Did he not know he was breaking his poor mother's heart? But as Regulus watched his older brother hastily drag his trunk down the stairs, ignoring his mothers screams ('Blood traitor! Abomination! Shame of my flesh! Good riddance! Good riddance!'), he realized that he must have been the only one who saw the pain in his eyes. And he realized, when Sirius turned to look at him with an apologetic grimace, he realized that Sirius loved him, and more than his parents ever could.
He had thought his parents loved him. But he was merely there to carry on the Black name. But Sirius would always love him.
That was what was running through his mind on his dying day. He was doing this, he was doing this for Sirius.
He became a Death Eater, to be a spy, to help stop Voldemort, for Sirius.
He was drinking this disgusting, evil, liquid for Sirius.
He was reliving his worst memories, for Sirius.
Because Sirius was the only one who had ever loved him.
It was done, it was over, and gasping, he wearily replaced the horcrux with the real necklace.
He gave his orders to Kreacher.
He could feel himself being pulled in, and Kreacher's screams, and the last thing he thought about was a time when Sirius was thirteen, and he was eleven - on his first train ride to Hogwarts...
"I'm so nervous."
Sirius grinned at Regulus' petrified face.
"'Course you are, everyone is," he said.
"Why'd ya come in here for anyways?" Regulus asked, "I thought you were mad at me for reassuring mother that I'd never get into a mudblood loving house like Gryffindor."
Sirius scowled at him. Then he sighed.
"I can't stay mad at you, Reg," he said, looking rather gloomy about it. Then he grinned and pinched Regulus' cheek, "You're just too cute."
Regulus snorted and batted his hand away. Sirius' grin remained for a minute, but it was all too soon gone, and suddenly he was looking rather solemn.
"Look Reg," he said, "I know - I know we don't get along too well sometimes, but I want you to know that"-
He broke off, staring at hands. He looked up after a few moments and started again.
"Well," he said, "Judging by your actions and words, you're probably gonna get into Slytherin and end up just like the rest of them."
Sirius said this rather bitterly. He went on.
"But right now your just Regulus, and you're my brother, and I - well"-
He couldn't seem to find the words to form what he was thinking, so he stood and clapped a confused Regulus on the shoulder.
"I'm just saying mate, that whatever happens, we'll always be brothers. I'll always"-
The words love you seemed to be on the tip of his tongue, but again Sirius broke off and removed the hand from Regulus' shoulder.
"Well," he said, "Well, I'm gonna go find James."
And with that, he left, leaving Regulus alone in the compartment.
Sirius was the only person that ever loved him.