I destroyed my bully's only memory of his late dad
Why would you destroy their memory even if they're your bully?
I forgot to last time I was there now he doesn't have any memory of his dad... I'll go now
You shouldn't be trying to destroy peoples memories of others. You never know how important that person was in their life and that's just extremely rude.
That student wasn't and he was just an asshole.
Sometimes go beyond just bullying. What you did was awful and he'll never have that memory of his father anymore. You have become the real bully in this scenario.