You should be nice to children.
Trevor saw Neville stumble as he tried to get up the stairs.
Trevor wants to decide what to do about Neville.
Trevor helps Neville stand up and them helps him get up the stairs.
Trevor walks away from the stairs and from Neville as he remains there stuck.
Neville thanks him for his help  and says that he was really nice to him.
Neville is stuck there for quite a while since nobody helps him.