You are absolutely wrong with your statement. His behavior was illegal at the time. I challenge you to read the court documents that detail the whole sordid story...

https://zh.scribd.com/document/358863553/Robert-John-Robertson-Court-of-Appeal-Case-2014bcca331

"While his sexual involvement with female students began while he was in the employ of the Richmond School Board, it is significant that it continued when he was in the employ of the Vancouver School Board. Despite having been caught by the police with a student in his car (in the midst of a sexual encounter), having been investigated by the police in relation to his involvement with other students, and subsequently having being brought before the Richmond School Board on the basis of his sexual involvement with three female students, Mr. Robertson continued his relationship with [Complainant A], who was then 15 years old. ... immediately after resigning from the Richmond School Board, he sought and obtained employment with the Vancouver School Board by intentionally misrepresenting the reasons he left the Richmond School Board.

It is significant that at the time he was sexually involved with these students it was a criminal offence to have sexual relations with a 15 year old of previous chaste character. At least two of the students were 15 years old at the time of the sexual relationships."