Responses
I'm betting on the teacher that molested him in his middle/high school years.
http://www.mangago.zone/read-manga/haru_ga_kita_kome_tasu/uu/haru_ga_kita_kome_tasu-chapter-2/29/
what if it's his father he ran away from a lot time ago and hasn't heard of him in years. So he asked his owner if he can find out were he is and found out he was dead. That's why he's seems so shook when the owner said he's dead......