My Adorable Betrothed

Leo, the son of a wealthy family, is the silent and shy adopted brother of the cool and regal Sui. When they were born, their parents predicted they would be wed, and after Leo's parents died he joined the family officially, but his relationship to Sui changed forever.

Living in the family home, the two spend their days having sex whenever and wherever they can. At Sui's parents urging that they get married, the two are forced to consider whether their commitment to each other is beyond physical.

(Source: TOKYOPOP)

Note: Chapters 6 and 7 were combined in the tankoubon release.