The Hero took my Girlfriend, So I took the rest of his Harem

The Hero and his Party sents off to kill the Demon Queen.

Y/n, and his girlfriend tagged along to help him. After a Long and Brutal Fight, The Throne room was open and the Demon Queen was there. But betrayal struck

The Hero stabbed Y/n in the back, Took his girlfriend and kissed her. Y/n, filled with rage, died with his final view was the Hero walking to the Demon Queen with his Ex-girlfriend.

But...He woke up 15 years before the Hero was summoned. Filled with a near bottemless rage and Hate towards him, He must train himself for 15 years and make him suffer for betraying him for all the help he did for him.

By taking his harem.