Ron and Al
Yeah, and your dad always blamed himself.
Voldemort and Crouch had always planned that Harry should win the tournament to bring Voldemort back to life. But your dad being who he was didn't think it was right to win alone since Cedric had always had his back, so Harry wanted them both to win.
And because of that, Cedric was killed. Even if Harry had the best intentions.
But the thing is, it really wasn't his fault. He was trying to do what he thought was right. And he had no way of knowing what could happen.