It was about a professor named ei who is a relationship with his 7 years younger childhood friend...the younger guy is working abroad in a coroner type of work i think. But the one who is super in love was the younger one. The professor have a box with a stone that was given to him by the younger ones.
In the flashback they first meet again in college where the younger ones finds out that everyone avoiding ei because he is gay and the professor incharged of overseeing ei thesis has stolen it instead.

I can't seem to remember the title...help pleasee

Takaramono wa Hako no Naka by Amasaki Yoshimi?