At first, girls called boys "Mr. Zhang San" in front of others, indicating that girls respected boys' occupation and status, while in private, girls called boys "Xiaoxin teachers", which may indicate that girls have a certain sense of intimacy and familiarity with boys.
The private address of girls has changed from "Teacher Xiaoxin" to "Brother Xiaoxin", which shows that the relationship between girls and boys has become closer. Girls may think that boys are older and can provide some help and guidance to themselves in some aspects.
The girl's personal address has changed from "Xiao Xin's brother" to "Xiao Xin", which may indicate that the relationship between them has become very close and familiar. Girls no longer need to add any respect or kinship terms to boys, but directly use boys' nicknames or nicknames to address them.