I remember reading comments in the past that talked about these things and was like "OHHHH that makes sense!" I unfortunately can't exactly remember what it was, I think it was something along the lines of he realized he had been forcing him into sex or something like that. It was definitely silly that they spent SO LONG not communicating, honestly comical, but if you think about it, if you were immortal and time wasn't an issue would you necessarily still be in a rush to resolve your problems? Like, you can address them whenever you want! As much as it would suck to suffer in that emotional turmoil for that length of time. I understood that part of it and found it interesting.
The "not explaining things fully/properly" is a common criticism of this work though. I just got done reading their other work, "Self-indulgent Vanilla" and it had the same problem. Definitely seems to be a weakness of theirs that I think if they worked on it their works would get taken to the next level.
Oh okay so I went and looked at it again, Adain said "don't look at me like that" because they were looking at him like he was a blessing and a god like his brother, he hated how his brother was worshipped and treated like a god. He also loathes humankind, does not want to help them and does not want to be asked for help from them.
I think the part of seeing Jonak as a child actually wasn't about forced sex (I actually forgot it was pretty consensual in this one) I think it was more he realized just how precious he was to him and came to love him unconditionally as you would a child, and he wasn't sure of how to process something he had never felt before.
if i may add, Adain also said that he became exactly what he despised about humankind. He realised he took advantage of Jonak when Jonak needed something from him. Just like how the priest took advantage of the orphan in Jonaks story. Adain seeing a young Jonak in a suggestive situation made him realise he was no different than the priest(humans)
This ^
It wasn't Adain seeing Jonak as something "precious" like someone would see a child.
It was his own guilt of having taken advantage of Jonak overlapping with the image of a child version influenced by the horrific story he had just heard.
I think some people were kinda over romanticizing the scene when it was clearly something meant to be disturbing to Adain. The look on his face wasn't confusion, but one of horror and realization.

This isn't bad at all BUT the story had quite alot of unexplained things, like why did Adain see Jonak as a child and stopped sleeping with him afterwards? (for DECADES btw). And because of the time skips and how long it took them to resolve things out it felt like they didn't talk to each other at all. Wdym you both have been feeling lonely for decades because suddenly y'all stopped sleeping in the same bed and none of you two bothered to ask why??? Also Adain's memory of when he was a child and told everyone to not look at him like that, what was that about? There's also the fact Lucius left his brother isolated, alone, thinking he was essentially dead (ik they can't die, he was sealed) for 300 years when that mf could literally appear any moment he wanted
I feel frustrated because this is good but at the same time it has many flaws that I can't mention because it'd take too long, anyway it was definitely worth reading even with all the things left unsaid