Geon has a lot of flaws but I don't think he's taking advantage of Sohm. The gross hyung was right that he doesn't really know Sohm very well, what he has for him is a big infatuation because he never actually hated him in all of years they were "rivals", but never took the time to know him well, he's mostly attracted to Sohm for the familiarity with his character and his looks. Geon is used to avoid his feelings and to get away from his problems, which is why he left, he was a jerk for the way he did it but his reasoning wasn't exactly wrong. The problem was that he can't communicate for shit, but he genuinely thought Sohm was going to be better without him, just like his bio mom.
Am i the only one who hates geon??? That hyung made me realize that he is indeed selfish and sohm is driven by the fear of geon leaving him so he does everything geon wants. and geon isn’t self aware that HE IS taking advantage of sohm.