
I think people forget that two things can be true at the same time! We knew a sad backstory is coming and obviously it doesn’t justify anything he’s done. But at least we’re gaining some clarity on why he is the way he is. I mean at least the author has been foreshadowing certain aspects of his personality like why he treats elders nicely. And I don’t care if you knew this was going to be his backstory cus let’s be honest we all kinda knew…

Did he just fuck a random old man

Based on the novel, he wanted to see if another man could turn him on, since he was always just attracted to women he thought something was "wrong" with him when he suddenly was turned on by a man. That's also why he smelled the man (Zhenya is obsessed with the way Taek Joo smells) and when he realized other men don't do it for him, he retreated.
He looked a little too fine in the bath