Read manga: Familiar

manga
Summary:

From bl-gyaru:After their parents' remarriage, Ryohei finds out Nanao, who has just become his stepbrother, is gay. Ryohei hates gays but in order to hold Nanao back from meeting his sex-friend, he bluntly says 'I will satisfy your sex drive instead of your sex-friend' and forcefully kisses Nanao.