Disclaimer: Not mine.
Beta'd by Dress-Without-Sleeves, who is so my minion, no matter what she says to the contrary.
Regulus knows he'll always be the lesser son, the one taken for granted. Though Sirius has betrayed his heritage, broken his parents' hearts, dirtied the Black name...he's still the one everyone talks about, still the one everyone admires, and Regulus is left hidden in his elder brother's shadow.
There's a certain bitter irony to it, that though Sirius is the Blacks' greatest disappointment, he's also their greatest achievement. Their parents are always telling Sirius to behave, to be like Regulus, but they also respect their older son in a way they never have the younger. To them, Regulus will always be the a cheap imitation of his brother.
Unlike Sirius, he is dutiful and obedient and does everything his parents tell him to.
"Grow a backbone," his father says, and Regulus hears an unspoken "like Sirius" tacked onto the end.
"Show a little pride," his mother orders, and her eyes wander to her first son.
Regulus wishes, sometimes, that he had the nerve to be like Sirius, to defy their parents and make his own way through life. And he can't help admiring his older brother nearly as much as he resents him.
And he strives to be better, to be the best, but only ends up a fallen second-rate star.