not the most popular hc but james was never regulus’ replacement to sirius.
james was his best friend, his other half, and someone who would always have a place in his life beyond romantic or platonic bounds.
remus was something else to sirius. remus was the love of his life, the only person sirius really listened to, and the feelings he had for him were unique to him.
now peter … peter was exactly like a brother to sirius. he looked up to sirius like regulus used to, he followed him around like regulus used to, and it was impossible for sirius to not have the same bond with peter that he did with regulus. that’s why sometimes he would snap at him, too, because that’s just how brothers are.
except peter didn’t have siblings so he couldn’t help but internalize all the off handed rude comments that sirius thought were just playful or would brush off. it didn’t help that sirius talked about regulus with such resentment and peter felt like he could relate to regulus so sirius probably hated him, too. all that contempt just kept building up.
and in the end, even though regulus was a death eater just like peter turned out to be, the brother sirius chose to have betrayed him in ways worse than regulus ever did. because regulus never had the power to destroy sirius’ life. sirius took that away from him the day he was disowned. he willingly handed peter that power, though, and it was a mistake that had consequences to it that none of them would ever heal from.
