Were you ever a bully and when did you realise?

I was bullied for 5 years by half the boys in my class. Was called a spack, retard, every ginger insult you can imagine, just repeatedly called stupid. Wasn't just names and being put down but cba elaborating into every instance. Even my closest friend talked to me like shit and she would sometimes join in. It was a very academic school and I think a lot of students were under a lot of pressure from parents, and they'd sniff out and target a few in the class to be their verbal stress-relief punching bag; to project all the shit their parents put on them onto others. So when a girl moved from another form into ours, after being bullied there, she became one of these targets. And I heavily regret that sometimes, to take some of the heat off myself, I'd join in ridiculing her behind her back. She wanted to be friends with me, my formerly mentioned friend, and the other who made up our trio. But I found her annoying and didn't want her as part of our group, so was outwardly just mean to her/not inclusive or welcoming. They called her "the Mammoth" because she was quite tall, chubby/bulky and a bit hairy for a girl. And I would call her that behind her back too. I felt guilty for it for years, then about maybe 5 years after I'd left school, I just decided to send her an apology message. Said I was sorry for contributing to the bullying and shit she got at school. She said she appreciated the apology and that it was a long time ago etc., but that she was thankful as no one else had since apologised. I wish any of the boys who bullied me had apologised for it, even if they did now I would want them to. It affected my self-esteem pretty irrepairably.