not 100% confirmed yet, but like I said in my very first comment, it could have been that the glasses senior heard the white haired guy outside the hallway and deliberately implied "let's have sex again" so that the person outside would overhear them.
Still, that top is not someone i, as a reader, could have faith in LOL he deliberately edges the MC even up to the latest chapter and we still don't know what his intentions are (if he even is capable of any???)— does he like MC that's why he wants to 'try' and have sex with him? does his attachment to MC even stem from romantic feelings or was it just because of their past that he wants to hold on to it? and so on.
Ofc, I would be the happiest among all readers if the top didn't sleep with the glasses senior. But still, I'm reserving that for when the author actually tells us straight to our face abt what happened that day (hopefully next chapter, since the white haired guy told our bottom they (top & glasses) did sleep together right after the top said they (top & glasses) did not).
im not sure abt that 'take it off' thingy during that chapter, it might be just a translation issue,, but that phone call in chapter 15 is glasses guy talking abt white hair guy, saying shit to youngha like 'does he miss me' or 'did he look depressed when im not with him' or smth, he's totally yearning for white hair guy imo
I can’t 100% tell you about that one because the author hasn’t shown us the full context yet, the translation is correct though he does say “take it off” (talking about an object or his clothes, we don’t know) BUT if i had to take a wild guess i’d say he was just trying to make the white hair guy jealous, hmo; they’re only talking casually about the cat that visits but the moment the glasses guy hears someone outside the door he suddenly changes the subject to that, in chapter 17 we learn that they are actually neighbors so i’m pretty confident the one he heard outside was the white hair guy - now, is he showing youngha porn videos or doing something else? we don’t know, but later on mc literally asks youngha if he slept with glasses guy and he says “no” so there’s that

the top did NOT sleep with the friend -___- (it was all a misunderstanding) i get that the author made the situation suspicious on purpose but have some faith on the top!!!!!