She left him with his dad if I remember correctly? And told him she was coming back but never did, and hyesung struggled a lot waiting for her and being with his dad and then she decided to come back when hyesung was older and had money I guess and he felt used
LORE DUMP to realize how fucked up this actually is (mostly from Dojin's side). Hyesung's mom abandoned him with his abusive dad so she could hook up with a new man and didn't take him with her because she didn't want her new family to know she already had a kid. The direct consequences for that were
1. Hyesung having to move out early so he could get away from his dad
2. Because he moved out he also had to drop out of high school and in this world there's already discrimination against omegas so I'm sure you can understand how much harder it would be to get a job as an uneducated omega
3. Almost getting tricked/forced into sex work multiple times
And this isn't even all of it this is just some of the worst stuff that really affected his life. In the main story when she comes to see Hyesung after she saw his face on tv they have a conversation about why she did what she did and she basically ends up blaming Hyesung for not seeking her out (he literally thought she might be dead) because the ABUSIVE dad said he didn't want to so she never, in over decade even tried to make contact with him. After this Hyesung kicks her out and says he's going no contact.
Dojin was witness to this whole scene and even comforted Hyesung afterward. Which is why this is all messed up. Yes, Hyesung did end up abandoning Byul for the first two months of his life (he has his reasons but that's not the point) however, that's where the similarities end he made an effort and he went back and has spent everyday loving Byul and trying to make up for it even with his new baby he still feels pain and regret when he remembers what he did.
If you are actually curious about his reasoning for leaving Byul. Hyesung was actually pretty young when he got pregnant after being raped by Dojin he was only 21. His pregnancy was very rough (it was a miracle it even happened) and birth was very painful and scary. So, with all the trauma, major life changes, plus a half formed bond/imprint (or something) he wasn't really in the best mental state then Heesoo got all up in his ear (I think?) and basically exacerbated his insecurities. Making him think that he was going to be a terrible parent anyway so he might as well just leave.
Omggg thank u sm for the detailed explanation
I read the main story long ago, can someone do a quick recap why HS hate his mom