You can’t change what you did, so apologise to your friend, then leave her alone. I think that you should move schools, to somewhere where no one knows what you did. People mess up sometimes, everyone does, but teenagers are particularly unforgiving of mistakes and this was a big one. I think you should see a counsellor to find out why you felt the need to bully this girl for fun, as it’s not normal behaviour. Then learn from it and don’t do it again. I can tell you from experience that being suicidally depressed isn’t fun. If I hadn’t had hell and medication, I probably would have killed myself when I was younger. It’s no joking matter.