I disagree. I don't think he opened the door because he believes Yashiro's arm is damaged. It was only about power. First of all he was angry but also, he needed to show him that he's assertive now and doesn't take shit from him.
It's a classic seme move that's been done a million times. The author is excellent at subverting BL tropes but they are still there.
I really love this analysis. Whether it is true we will see in march.
Did you notice that there is on object on the wall beside the sink that is always blocked by dialog bubbles? Domeki looks at it on page 36 and the next scene is even the sink behind Domeki. After looking at the sink, he seems to have made an decision and faces Yashiro again even though he saw the phone call of Inami.
Me and my favorite roommate noticed something about Doumeki in the last chapter, that could show us, that he actually did not change at all and is just as devoted to Yashiro as before. (now he is just better at acting)
We all know that Yashiro is blinded on his right eye and we now will see that he has trouble with that.
On page 19 Y reaches for the door handle but due to D's "Do you need me to rub your back for you?", Y turns left to look at D and misses the door handle.
On the next page Y reaches for the door handle again and misses again. Doumeki in the next panel only stares at Y with a (...) dialog bubble.
Doumeki waits at the doorway when Y showered and says "Just in case. I will leave when xou are done". From this we can tell, Domeki 100% noticed something was wrong.
On page 27 and before Yashiro praises Doumeki "but that's none of my business". None of my business. None of these should I care. He wants to leave asap and cannot stay there another second. He puts his hand on the handle.
And then I noticed something: THE TITLE PAGE.
Nanahara once told D: "Boss may not be able to use his righr arm anymore. He need a right arm for him [...] you hot it? Stay by him. Protégé him."
We see on a lot of pages, that Y has scars of gun wound on tge left shoulder, right elbow joint and abdomen and that D noticed them hence he always peeps at Y (we can argue he just peeps at him, because that's just how it is, but I think this means more right now).
ON THE TITLE PAGE what Doumeki was gently holding, is in fact Yashiro's frickin RIGHT HAND.
Doumeki saw, that Yashiro had trouble reaching for and holding the door handle and mistakes his arm wound as the cause! He seemingly aggressively opened the bathroom door. But not (or mot only) because he was angry at Y for, in his view, having sex with the disgusting detective (this is actually another topic: does Y really have sex with him or are we deceived by the mangaka) , - he was opening if for Yashiro.
Doumeki did not change at all.
His love and sweetness for Yashiro will always remain.