He was 20 in Korean age, so 18-19 in calendar years.
Luna was an accident, too. They had no idea he could still get pregnant.
The difference between Byul's and Luna's conceptions is that, like you said, Byul was conceived and given birth to from an act of sexual assault and baby-trapping. Meanwhile, Luna was conceived and given birth to when Hyesung was no longer literally grasping at anything to live another day, and now knows how to raise a baby from raising Byul.
He had literally no support system or anyone to truly lean on when he was pregnant with Byul. Of the two people who knew of his pregnancy, one was trying to baby-trap him, and the other was victim-blaming him for literally trying to just survive.
Fuck, honestly if i was in Hyesung's position, I wouldve killed myself long ago.
Oh my gosh, I also forgot to mention that on top of that all, he was literally told only weeks prior to becoming pregnant that he wasn't an alpha, but an omega. He had discovered that his whole life was a lie and was having an identity crisis
Hyesung is truly one of, if not THE strongest character/s in this whole series.
Shut up i totally forgot about that
NOOOO MY BABY HYESUNG JUST DIVORCE DIVORCE DIVORCEEEE
Lets not forget Byul was lowkey conceived from rape guys Hyesung was literally 19-21 (i havent read the love is an illusion in so long but im pretty sure Dojin took advantage of Hyesung's heat (?)) like.. u gotta think.. if u were in his situation u'd wanna make the most out of it and benefit from it urself because UR CARRYIGN A WHOLE BABY like i wouldve tried to abort too no doubt and obvi i understand byul too like id be distraught to see my mom having a planned baby while I was like an accident but man i cant even excuse dojin idgaf ab him anymore just divorce i wanna see him grovel and regret thx a lot