I think is because of the baby, I don't think Hyesung "loves" Dojin. In my opinion, hyesung appreciates what Dojin told him (That time when Dojin told him he will protect him and that's when the bonding happened blah blah) I think Hyesung realised that he needs his son and I expect him to take care of Byul and his relationship with Dojin will improve because both will have to look after Byul. Just guessing, maybe F*arg*o will do a plot twist, who knows
Not all couples love each other deeply, it happens all the time unfortunately
This chapter does not make me happy. If he wasn't bonded with him would he have comeback? Is he just with him because he doesn't want to die? I really question his love.