
I believe it was one of his clients, the "prince" one that pierced his ear without consent as a way to permanently mark him or something. So its a way to show how being a call boy is eating away at him and how others think they could use or leash him to them. Haru said in the beginning how he wanted to spoil someone for real. So those panels where he is with Hiroki show hes real with him with the stark contrast of reality with his other clients. I'm assuming the ear piecing is more like a scar (mentally and physically). Especially since we've never seen him wearing an earing yet.

Ah so I did a little online digging and this story is still ongoing with chapter 5 schedule to release sometime soon according to this site (Just the delete the space)-->
https://www. cmoa.jp/title/202257/
What’s with the ear piercing flashbacks in the last couple of panels?