Sure technically he did abandon Byul but he left for 2 months after he gave birth. Byul doesn’t remember and wouldn’t even know if he did not overhear his parents talking about it. Hyesung never made Byul feel unwanted. That’s disgustingly incomparable to grandma leaving Hyesung for all his childhood to her ex-husband who she’s very much AWARE that is an abuser. 
Like i too learned that i was an accidental kid pretty early on in my childhood, and i learned that my existence fucked up my mom’s plans (they were poor af) and that she planned to abort me but didn’t in the end. Never in my life did i thought that she “abandoned” me or that i’m disappointed in her for thinking that way. I’m actually more proud of her for surviving while still raising me as a good mother. 
That’s all the more reason why i can’t empathize with Byul choosing to connect with grandma. Because my mom is the most important person to me, and i can’t for the life of me imagine cozying up with someone who i KNOW hurt my mom so deeply, even if there’s a good reason for it. My loyalty is with my mom, period.                                            

		
Byul shouldn't have said that, hyesung, really tried to do his best after all the trauma