The Servant I Bullied Rose to Become a Great General

Wen Fuyu is a pampered rich young master. At fifteen, on a whim, he bought a study companion at the black market and bullied him relentlessly. Ten years later, the once poor and inept study companion has risen to become a mighty general, while Wen Fuyu is sent to the general's residence as a pawn for his family to curry favor with someone powerful.

A vengeful general × a pitiful young master

The synopsis doesn't cover the whole story. Things take other turns later on, and it's a sweet romance.