And people who are in positions of power over minors have a higher responsibility placed upon them for a reason. And this is the reason whether actively or passively he has abused a position of responsibility. The age limit is there for a reason it's the law - he broke it.
You walk past a car with the door open and the key in - you say hmm nice car I could just take that you know - and yet you do not.
Now you're the one coming up with ridiculous analogies

Stealing a car and having a relationship in this instance are completely unrelated.
I'm not disputing the fact that the law is there and that there is a reason for the law. I'm just saying that it doesn't produce a fair outcome in all cases. It could be potentially destroying a man's life and a perfectly functional relationship. This would have a negative impact on the girl who the law is supposed to protecting, assuming it is all consensual.