I think in terms of storytelling, it’s being used as a way to showcase how jiwook is detached from all things sexual, which is why when hyun asks why jiwook is impotent at such a young age, the story segues into all the trauma jiwook endured between the timeskips of the story. his lack of a physical reaction to a situation some people may register as sexual (even if they did not want it, there are still often physiological reactions) is in direct contrast towards hyun’s youth and urge for sex. its both to show how much time has passed, what has happened to jiwook, and arguably how close the two are as roommates.
Thank you so much for your reply, now it makes sense to me!
I have so many questions but I'm going to ask just one, Why did Jiwook do a handjob for Hyun when they were roommates? I mean I don't care about the handjob or even if they had sex, I mean what was the point? I didn't get it at all and it bothers me!