Growing up you are always told that turning of age is some big milestone and that becoming an adult is this great accomplishment. So why does it not feel like it? With all the importance that turning of age and growing up is given why isn't there some great feeling or change that comes with it?
So why does the only thing Sirius feel is regret? They just graduated he turned 18 less than a week ago and all he can think about is all the opportunities he missed, everything he didn't do.
Did Sirius do something wrong? Was there something he missed? A girl he didn't kiss? A party he didn't throw? A prank he didn't do? Why wasn't he feeling complete? Why can't he shake this feeling that there's something he missed? Or someone?
He had done everything right! Attended all his classes, made friends, made the quiddich team, danced and drank all night, kiss half the girls on campus. But still he just felt like something was missing.
He had made mistakes along the way but that's what growing up was about, wasn't it? Maybe his shunted emotions were to blame, maybe he was just so used to suppressing any feelings of joy that he had forgotten what it was like to feel whole. He had been whole in the start when he first got to Hogwarts. When he could laugh with Remus smiling so hard his jaw ached or play around with James on their brooms and felt his heart glow or when he and Remus used to climb into each other's beds and talk or smoke.
When he was younger everything was easy and he could let his mind and heart talk aloud, but then came the feelings and the hormones of puberty. Then came the heat in his cheeks when Remus would laugh at something he James or Peter had said or the dreams of the other boy at night that left him afraid to close his eyes. Then came the lack of feelings for girls and the realisation that Sirius could never care for a girl in the way James care for Lily. Then came the nauseating fear that with every look, every touch, every smile or blush in Remus' direction would give away his abnormalities, his disease.
So that meant no more belly laughing, no more smiles that reached his eyes, no more late night talks with Remus. It meant more girls, more parties, more booze. Enough to forget or pretend to. He buried himself under this disguise of who people wanted him to be- who he had to be.
But still the dreams never went away, nor did the memories of the nights when he could live fully without shame. With them came reminders of what he was missing of the cause of all his regrets, and of what he could have had if he hadn't coward away from who he was, what he was.