Childhood Friend of the Zenith is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

Gu Yangchun, who betrayed the Orthodox sects, became a demonic human under the Heavenly Demon. Living as a demonic human, he led a life filled with regret. He committed countless evils not of his own accord, but under the orders of the Heavenly Demon. In the Great Orthodox-Demon War, thanks to Wi Seol-ah, who cut down the Heavenly Demon that made even the three supremes of the Orthodox forces kneel, Gu Yangchun was taken prisoner by the Orthodox forces and suffered for his sins. With whatever morals he had left in him, he died giving Wi Seol-ah information about the Demon Cult due to a bind the Heavenly Demon had placed on him. Then, for some reason, Gu Yangchun regressed to when he had first met Wi Seol-ah. Realizing the regression was not a dream, Gu Yangchun decided to live a quiet life. However, bad ties from his previous life began to draw near, one by one.