There are a couple ways I would go from here. First have the bully as an older child (let's say high school) maybe reflecting on how he could have been better. I don't think you want your main character to be an out and out bully. People won't respond. I would have the main character be maybe a bully because he was being bullied himself and he felt like that the only way to make it stop. Or he could be friends with a bully, and participate in some of the bullying, but really know it's wrong.
Either way I would start with a single person on stage, lit by a solitary light, my first line would be, "Words alone are not enough to say how sorry I am, if I could take it all back, I would."
Then you have several options.
1. He has learned the kid he bullied ran away, had thoughts of harming himself, etc feels responsible
2. He is in serious trouble, either with the law or the school and loses everything due to his bullying. (still need to put in about how he knew it was wrong to bully, but maybe went along with the crowd, and now they are all in trouble)
3. Maybe the bully moved to a new school. Now he is the victim and has first hand knowledge on how horrible he was.
I think scenarios should end with him facing the kid he bullied and offering a sincere apology. The bullied kid should accept, but let him know that bullying will only truly stop when kids stand together and not allow it to happen.
I am a writer, but not a play writer. This was just some of the scenarios I had pop in my head.
ETA: Renee, nope not intentional. Never even heard of it before. :) But, there are only so many scenarios that you can do with a bully situation and all of them have been done over and over again. It's like what we know here, there are no real new stories, just new versions to old tales. :)