Am I the Asshole for revealing why I rejected a “promposal” nearly 10 years ago?

I (27F) attended school in the UK. Towards the end of our final year of school, when we turn 18, our schools organise something called a Formal, which I suppose is a bit like a prom without the romantic aspects as you’re not expected to go with anybody, and the idea of promposals generally isn’t something that’s done here.

Nearly 10 years ago, as I was preparing to leave school, I found out that, not only did a boy in my class have a massive crush on me for years, but he was planning one of these massive “promposals” that are often done at proms. He had always been a horrendous bully to me. He would go from calling me hideous and claiming that I would die alone and unloved, to stealing my friend’s phone to get my number, or sneaking up behind me and cutting out strands of my hair that to keep, or going so far as to find my house through my father’s distinctive car.

Naturally, when the day for his “promposal” came along, he came out with his sign in front of the entire school, and I bluntly said no and walked away. I don’t like confrontation or arguments, but I had no intention of sparing his feelings after all he had done, and I was honestly just uncomfortable and wanted to leave. He badgered me until the day I left school for turning him down and being heartless. His friends did the same. I didn’t care.

I recently met one of his old friends in my old town. I went to the business where one of them was working, and he kept bringing this up, saying that my bully had gotten depressed after we left school and hadn’t dated at all because he was embarrassed from the rejection and was still hung up over me. He kept asking me why I felt it was OK to reject him like that over some nasty words, and if I was really that petty. I got sick of it, so I told him. Turns out that, because all of these creepy things had happened within the classroom, he hadn’t seen them, or even heard of them happening. His friends and my other bullies within the class were covering for him. The friend abruptly left without a word, but apparently, the gossip did the rounds.

Now, the friend group is divided in two. Many of those who didn’t know are pissed at him for lying, and pissed that their other friends hid what was happening as they think it went too far. The others are pissed at me for airing his dirty laundry. His parents apparently also know now, and they’re pissed that he had their sympathy through lies, and now know that he practically stalked me, which brings up questions about whether they want him to take over the small farm vs a younger brother. I wonder if I should have just let his friend be mad at me. I’d probably have never seen him again, anyway. I didn’t know that he would tell anyone as he’d never been one for gossip that I knew of, but I also didn’t expect this to potentially ruin the life of someone I haven’t seen for nearly a decade.

AITA for telling his friend the truth about what happened?