Responses
She abandoned Hyesung with his terrible dad which led to him not being able to finish school and almost being tricked into working in a brothel. When confronted with Hyesung's anger she said "you didn't come looking for me either".
My guess on why her new family left her is cause they found out she had and abandoned her child before marriage and didn't wanna be connected to her in case anyone did some digging. Imo it's karmic justice those years Hyesung spent alone in his youth are being given back to her in her old age.
Byul is probably too young for his mom to dump all the trauma he faced with his grandma so byul doesn't know maybe? Reminds me when I became old enough and my mom told me everything her family and my dad's side of the family had done to her and oof it became my villain origin