This needs to be said, over and over and over again. I had friends in high school and outside school, who were slut-shamed. It was awful and devastating to them. Boys were never called names, they were given badges of honor. I never understood the double standard.
And when it comes to adult/child relationships... it's never right. Even if the young person wants it.
This story also has the double-whammy with the power dynamics of a teacher and student... like a worker and a boss. There's a reason that there are rules against these things.