You answered your own question.

Your boss is not a "nonessential" person, nor is your personnel file.

The statements have not been harmful to you--aside from offending you personally that someone else could think this of you. You are GUESSING that at some point in the future it MAY harm your reputation .

And the statements were not malicious. They were constructive. This does not mean they are ACCURATE because they ARE opinion. It means they are constructive. It is their JOB to teach and inform you of how to be the best teacher you can. They are TELLING you that this is an area that CAN, in the current political landscape of inappropriate behavior between student and teacher, become potentially a problem.

They have to protect themselves as well. If they FAIL to document things they FEEL may potentially be a problem if NOT addressed, then THEY could be liable.

No one has asserted you have done anything wrong. You don't like their comments and are offended by them. I understand that. But in all truth, everyone who has ever held a job has had this type of interaction with a superior who they felt was wrong in their assessment of their performance.

You are there to learn. Take it with a grain of salt. If it is a valid observation, learn from it. If it is not valid, and is entirely off base, learn from it.

Bottom line--nothing you have said remotely fits the definition of malicious slander told to a third nonessential third party.