I looked it up... and I understand it.
Some bullies have problems which they're forced to face on their own, such as parent abuse and emotional problems. As a result, they bully other people, transferring their problems onto them. As described in the show, some bullies may develop sexual fantasies about other people, which is most likely caused by sexual abuse by parents.
As a result, they become suicidal, and are unable to get help. But by being unable to get help, and bullying others, they are unknowingly causing the victim to become depressed, eventually leading them to either hang themselves or jump off the school roof.
Then again, it's not the bully's fault for the suicide of the victim, it's the parents fault for causing them to abuse the victim to their own death