Blake is always pure.
Therefore, although the Black family has a prosperous family, there are large and small black marks on the Black family tree.
It seems that every generation of the Black family has an expelled heir.
Regulus Black.
The second son of the Black family, he has an excellent elder brother, but his parents always subconsciously ignore him. He is only the second son, and it is easy for him to be ignored, especially when there is a smart and excellent elder brother above him.
He was used to silence, used to being ignored, and used to being alone.
When Sirius rebelled and abandoned his responsibilities as heir, he was forced to take up that responsibility, all for Black.