This can be a spoiler I dont know

He is upset that Misumi favoured Yashiro over him.

In case that was misinterpreted, Misumi and Hirata are regarded as brothers in their yakuza family. Yashiro is their son. Hirata basically feels that Yashiro has been handed everything to him, by the person he idolises, and he thinks this is an injustice. So no Hirata doesn't "love" Misumi in the sense of wanting to sleep with him. Saezuru deals with the topic of unrequited relationships, not feeling validated or recognised not just in a romantic sense, but familial or as workmates.

Here's another post to explain their set up.
Misumi is deputy leader of the Doushinkai, which is the head group. He is also Acting Chairman and wants Yashiro to replace him as deputy leader.

Hirata is leader of the Shinseikai sub group. He wants to be deputy leader of the Doushinkai, and has hated Yashiro since he first set eyes on him. He knows Misumi is planning to seat Yashiro on the executive board so is colluding with a rival group who share ties with his own, and was planning to defect. Killing his family members due to his hatred of Yashiro, just like he killed Kurobane, as he felt he was getting in his way of Misumi who also represents a way to get promoted.

Yashiro, Waka or deputy leader of the Shinseikai. Misumi's "favourite", but a competent leader in his own right. Misumi wants Yashiro to replace him as deputy leader of the head group, but Yashiro wants to either leave the yakuza or remain in his current position.

Sorry, I made a mistake with the yakuza family. I'm re-reading it, and Misumi is Hirata's parent (not his brother). Also though, to add to the confusion Hirata is currently Yashiro's parent (so Yashiro has had both Misumi and Hirata as his parent, whilst being in the group).

So it would look a bit like this for a family tree:
Misumi (parent)
Hirata (son)


Misumi (parent/ maybe not currently)
Hirata (parent)
Yashiro (son)


Okay that's enough from me. (⌒▽⌒)

Nope, I was right the first time. Hirata is Misumi's brother, but he wants to be in the same position as Yashiro ie Misimu's son (Yashiro is Hirata's son currently also).

So it would look a bit like this for a family tree:
Misumi (parent)
Hirata (brother)

-Yashiro's immediate family tree not including brothers.
Misumi (parent/ maybe not currently)
Hirata (parent)
Yashiro (son)

FFS (It's late) Here is an another edited version.

Misumi (brother/ higher rank)
Hirata (brother)

Misumi (parent)
Hirata (parent)
Yashiro (son)

Yashiro is also brothers with Ryuuzaki.

That's all I can remember right now without having to re-read it, so have probably made plenty of mistakes. Just wanted to make a final post of what I meant to say the first time, seeing as we can't edit. (▰˘◡˘▰)(▰˘◡˘▰)(▰˘◡˘▰)

Thank you man now everything is more clear

Here is the part where Misumi says that he and Hirata are brothers within the group http://www.mangago.zone/read-manga/saezuru_tori_wa_habatakanai/mf/6ba770cf8927a77ff194ed50229a1153_chapter-5/pg-24/

I see. After a few chapters I was just focused on Yashiro and Doumeki soo... thank you again.