He didn't rape him because he wanted to. Omegaverse is chaotic. They act according to their pheromones most times. So it wasn't rape and he begged hyesung to keep the baby and the idiot made a deal to collect money after birth. He choose to make the deal no one forced him to.... He left but he couldn't leave because of he felt guilty not just because they were bonded. Read the manhwa properly...
Read the manga properly, yes, please you do.
Dojin is a (n extremely) dominant alpha and Hyesung is a (n extremely) recesive omega. If he wants, he CAN resist this omegas pheromones. AND if the issue is the rape and the pheromones, there's this couple of times when Dojin forced Hyesung to have sex even though he wasn't in heat, the most notorious one is when Hyesung tried to leave to go live with his friend "Tofuface".
And... Now I'm too lazy to continue with the baby issue... Maybe later lol
This whole storyline as it starts out is actually really dark. Both of them start off as really problematic I mean the seme rapes the uke just because he wants him to stay then he uses the baby in order for him to stay with him but even after that when the uke tries to leave again he cannot. The only reason why he stays is because they were bonded and he cannot survive without him. Ik they get better but I cannot get over this fact.