Read manga: Twilight Outfocus

manga
Summary:

Tsuchiya Mao is roommates with Otomo Hisashi who is secretly gay, that's why they made three rules:
I. Mao must never reveal Hisashi's secret
II. Hisashi won't look at Mao as a romantic interest
III. Neither of them can get in the way of the other's "personal needs"

They had no problems living together until the movie club - which Mao is part of - decided to do a BL movie for their school festival project and casted Hisashi for the lead role.