im desperate, help me find this one

a few years ago i was reading this korean webtoon i think it was and the story line involved this blonde fl that ended up working for the ml as a maid, they knew each other since kids but they weren’t supposed to interact or sum like that and he was a young master (or just master idr) and had this core(?) that looked like a gem and it was black and it was corrupting him if i remember correctly and it was so incredibly interesting and i can’t remember the name ☹ and i also hope i didn’t hallucinate this one bcuz it was absolutely incredible