I agree, tho.
One of the reasons I believe—among other things—that the brother and Ideum's crush are the exact same person is that they were mentioned right after next to eachother. A whole chapter was around this– Immediately after Ideum had the flashback/dream about his school crush, Jaeyi's brother was brought up, so I find it hard to believe it's just a coincidence. Unless, of course, the author is deliberately trying to mislead us for a bigger plot twist. I can’t wait, I feel like a detective at times like this, lol.

Jaeyi’s older brother, Jiseong (the swimmer) was Ideum’s school crush, (maybe, but I still believe he was, and they are the same person) but the dude in school looks different than this one (but maybe because he dyed his hair, wear contact lenses, or when Ideum had a flashback in his dream, he imagined Jaeyi’s face on Jiseong) but nobody really knows what is the truth now, I still think the swimmer was Ideum’s school crush, but maybe this is why Ideum didn’t recognize him, because his memory is foggy, or Jiseong changed his look. But when I tryed to find more clues, I found some theory. Like, maybe Jiseong is the one person who is stalking and leaves bad comments in Ideum’s BL writings, or Ideum wasn’t able to go to school because of his surgery so he had to go later, and the schoolmate was Jaeyi and when Jaeyi first got in Ideum’s apartment he was interested in his books and in his novel (like in school, what is he reading). Etc. But Jiseong, already knew Ideum’s name, and the other swim teach’ noticed it too. Jiseong took so many things from Jaeyi, this was mentioned before too in prev. chapters, maybe the swimming past was also stolen from him, maybe this is why the other swimming teacher knows him so well, or because of his brother a swimmer, idk.
Also, Jiseong said, he wasn’t swimming a while (for 3 months I think) and I think Jaeyi didn’t know that his brother would be there.
We have to wait what is the truth. But the plot is plotting.
And Jaeyi. You are in love, It’s time to realize it, even tho you said, you didn’t understand feelings like this, you never acted like this with others. C’mon!