Lovers in the Night(1997)

Ai to wa Yoru ni Kizuku Mono

Hired as a servant by an Aristocrat family, Claude works hard to care for the family that took him in. But when the master of the house and his wife eventually pass away, Claude must keep spoiled son Antoine in line and teach him to be a proper gentleman. As the two become closer, a forbidden love develops between them...

(Source: BLU Manga)