The manga you're referring to is titled "Maou wa Yuusha no Kawaii Yome: Party no Bishoujo 4-nin kara Uragirareta Yuusha, Maou to Shiawase ni Kurashimasu" (The Demon King is the Brave's Cute Wife). It follows a hero who was betrayed by his female party members and subsequently finds happiness living with the female Demon King.
Introduction: The Phenomenon of the “Reverse Villain” Genre The manga you're referring to is titled "Maou
However, Shion survives thanks to the unexpected intervention of the Demon King, Villa (or Vira), who rescues him from the brink of death. Shion begins a new life in the Demon King's realm, discovering that the "evil" ruler is actually a doting, affectionate girl who wants nothing more than to live happily with him. The Turning Point: Chapter 5 and "Karma" Shion begins a new life in the Demon
—that befalls the ungrateful party members. The central theme explores the concept that true loyalty is rarely appreciated until it is gone, and the consequences of betrayal are absolute. The Narrative Setup: Betrayal and New Beginnings The Narrative Setup: Betrayal and New Beginnings Public
Public Backlash: The world begins to realize the truth about the "Hero's disappearance," leading to the four former party members being branded as criminals and facing global condemnation.
Kael (Chapter 5, Repack): “Let them rot. I’m not a hero anymore. I’m just... his.”