Forgot the name of a Yaoi Manga

Please help, I think i'm going crazy trying to find a certain manga.

Story is based off how the MC took a brooch from the younger man he was teaching/mentoring. The brooch's gem is purple, same color as the young man's eyes.
Its revealed the brooch is used for succession when he's older, so when that time comes, everyone is chiding him for having lost it, so he can't succeed his family's lineage correctly without it.
MC goes back to return it, as he feels bad about it.