As Long as We Both Shall Live

Saimori Miyo was the unfortunate child of a loveless, arranged marriage. After her mother died, her father brought in his lover and her own daughter, Kaya. From then on, Miyo's life was reduced to that of a mere servant. Even worse, while Kaya inherited the family's psychic abilities, Miyo had none—she was truly the daughter with no merit.
After years of being treated like dirt, Miyo has learned to keep her head down, hide her pain, and obey every order. So, it comes as no surprise that she is arranged to be married to Kudo Kiyoka, a military captain rumored to be so cruel that he has driven away every one of his potential wives so far.
From a painful upbringing to a painful marriage, that's the future that awaits Miyo—or so she thought. Contrary to her expectations, her new husband is actually kind-hearted. What really awaits Miyo is a blissful, everlasting marriage full of happiness!
(Source: MyAnimeList)
~~ Adapted from the light novel series "Watashi no Shiawasena Kekkon" (わたしの幸せな結婚) by Akumi Agitogi (顎木あくみ).