Dry Heat(2001)

Warera no Mizu wa Doko ni Aru

Little Tatsuhiko, says to his young family servant Itaru,"when I grow up, I want to become a politician and change the law - so two men can get married. Will you marry me then?” Ten years later, Tatsuhiko leaves a mysterious note behind and disappears from his prestigious academy. Itaru is asked to find him, only to discover that time changes people and learns that things aren’t the way they used to be... From Yugi Yamada, creator of Close The Last Door and Laugh Under The Sun!

(Source: Juné Manga)