Textbook of Revenge is a Manga/Manhwa/Manhua in english language, Seinen series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.nl fastest updating comic site. The Summary is

Yotarou Kurose dreams of becoming a teacher, looks up to his homeroom teacher Shiratori-sensei and is subject to gruesome bullying. One day, fearing their actions have been exposed the bullies tell Kurose on the rooftop, "Before we get found out, why don't you kill yourself?" Terrified of what was happening Kurose loses his footing in the commotion and falls... "Hey, teacher. Can I do this over again?"