Depending on local laws, fondling or unwanted sexual touching can indeed be a criminal offense. Certainly in the US and Canada it is. Not sure about OP's situation because we don't know on what Caribbean island these incidents took place.I said his actions were unprofessional. He actions were childlike. I don’t see a criminal situation. I expect people to act appropriately and not misuse their authority.
His actions go well beyond "unprofessional." Unprofessional conduct would be things like berating students, yelling at them, demeaning them, etc. Rubbing your genitals against someone's buttocks without their consent is WELL past that.
You are essentially victim blaming. You are saying "Well, OP didn't say or do anything to stop it, so the predator might have gotten the impression it was okay to keep going." BS. This instructor knew full well what he was doing was wrong. But he also knew that the way in which he was doing it - pretending that it was part of a skill to be taught, checking her buoyancy, etc. - could give him some amount of "cover." That is absolutely predatory, with malice of forethought, and smacks of someone who has done this many times before.
I'm sorry, but I will not simply agree to disagree on this point. This was 100% on the instructor.