Responses
He had no choice but to go back since if he's apart from Dojin for an extended period of time, he'll die. I don't think Hyesung went back to Dojin because he cared for him, (though he's starting to care more for Byul) but because he physically can't run away to wherever he wants to go due to the bond. He could be crying because he has no choice but to stay with Dojin, even if doesn't want, not to sure because the hug could be interpreted differently. So I wouldn't say the issue is fully resolved, there is still the fact that Hyesung doesn't love either Dojin or Byul enough at the moment ti willingly want to stay and a be a family with them.
Was that all it took? Well, whatever as long as Hyesung and Dojin be good parents to baby Byul. Especially Hyesung, he can still redeem himself and be there for Byul and a good lover to Dojin.