We can take a guess that he didn't have a good relationship with his father (who thought hyesung was an alpha) so now that's he's an omega, it'd probably be horrible (in his mind).
Also since he's said that he's always alone and had to live with it, he probably doesn't believe in dojin's love and doesn't wanna stay or he thinks it'd be real but he doesn't wanna be in that situation because of stress or not used to.
I'm anticipating when we'll truly see what's the deal with him. I wonder how he is so good at math even if he (apparently) sucks at other things.
That's what I'm thinking as well. I want to find out more, that's why I'm still staying around. Even though the past chapters are breaking my heart.
I'm sorry, but I'm still confused as to why Hyesung still wants to leave? Does he really hate being an omega? I wish the author shows more of his background.