Hyesung remembers the events of Byul's life in great detail, even the detail about the kid who used to follow Byul in kindergarten that's technically been so long for them. It proves that Hyesung really treasured Byul to the point that he even remembers the kids around Byul. He treasured him More so, since he still feels deep regret for leaving byul once, even though he knows byul doesn't remember that part of his life, hyesung still repented for it (even when no one was condemning him at that time). Once he vowed to be a good mother to byul, he really followed through.
Hyesung remembers the events of Byul's life in great detail, even the detail about the kid who used to follow Byul in kindergarten that's technically been so long for them. It proves that Hyesung really treasured Byul to the point that he even remembers the kids around Byul. He treasured him More so, since he still feels deep regret for leaving byul once, even though he knows byul doesn't remember that part of his life, hyesung still repented for it (even when no one was condemning him at that time). Once he vowed to be a good mother to byul, he really followed through.