I think it's just a translation error, may be something along the lines of "I think I love you" or something, just guessing though
I already replied with this to someone else, but it fits here too, it really is a translatiom error:
He did declare his love, in the raws he says “johahaeyo, hyung” which actually means I like you, and he is thinking about liking him not falling in love with him, I don’t know why did they translate it this way.
Ahh this clears it up a lot. They really should have just left it as "I love you", sweet and simple. Maybe it felt a bit sudden for them ? I felt like the suddenness expressed Sangwoo's feelings better. I also kinda wish they wouldn't omit the "hyung" so much either. I feel like this is a bit of a problem with official translations, they modify a lot of stuff so it sounds "better" or more cool, but in the process a lot of things can get lost in translation.
Yeah I think the simple "I love you" made more sense with how he has a tendency to think about things when just blert out anything that comes to his head. The suddeness of it felt right like he was freaking out thinking about their relationship all together then randomly his mouth moved in it's own to say it. Lol
Did it go from "I love you" to "I'm falling for you" in the next chapter thats not the same thing at all....which is it (╯°Д °)╯╧╧