18+ Yuushazuma: Yuusha ga Shitekure Nakutemo, Seijo wa Kedamono Maou ni, Musaboraretemasu

Saint Iris finds herself deprived of sex by her husband, the brave hero Yuri, who seals her with a chastity belt. Living a life devoid of intimacy, she encounters a fierce man akin to a demonic beast. His name is Magres, the demon king who rules the demon realm! Thus begins an immoral love story in another world, featuring the sexually harassing demon king, the neglected saint, and the emotionally abusive hero!

(Source: MangaDex)