Because the vast majority of us never have to go through a "how not to be a fucking evil son of a bitch who emotionally tortures people for shits and giggles" stage when learning how to human during childhood and adolescence. For what OP did, he deserves to be riddled with guilt. He deserves to have flashbacks that haunt him. He deserves to lose sleep. He deserves to always feel like he's a horrible person who doesn't deserve happiness. It hasn't been so long since I was a teenager that I've forgotten those days, and not even the worst people at my school did something as heartless as what OP did. You have to be fundamentally broken to be not only willing but eager to try and inflict that kind of pain on someone.

OP, you ruined a life. No amount of apologies and no amount of remorse will ever come close to undoing even a fraction of what you did. You took a kid who was already alone and vulnerable and tried to make him feel as weak and worthless as you possibly could. Sending an apology was another thoughtless, selfish act because it wasn't for him. It was for you because you wanted to alleviate your guilt. If you had any sense at all, you'd have stayed clear of him because the last thing he needs is for you to remind him that you're still out there somewhere in the world. Don't contact him again, and don't even dream of asking forgiveness. You don't deserve it and you know it.

You want to do something right for once? Dedicate yourself to anti-bullying efforts in your community. Contribute your time and money to working toward a future where fewer children are tortured the way you tortured Jack.