Ohigara mo Yoku

From Shinmakoku Scanlations :From the time he was very young, Shuuta longed to be "married" through adoption to Kouhei. While Kouhei as a guardian was too absentminded, Shuuta always felt as if he never fulfilled his duties as a "wife". It's a love story between an airheaded, thick-skinned, handsome "husband" and an innocent, pure-hearted new "wife" with an age gap!