
I think Hajin is her son she just hate him in my head cause the marriage was probably something was pushed on her and she thinks is Hajin's fault even though is probably her fault and Hajin's father fault
I think the other boy is the son she had with someone she loved or the son of someone she loved I have a lot of theory's I gonna need a 4 hours videos to explain everything

Disregard my previous comment, I really do think there was a child swap.
- no photos of Hajin before primary school
- According to the MC, Hajin "should" have lived abroad until he was 5.
- Hajin as a child had a Busan accent
- Chapter 34 Baek Ha-yeon was born in Busan, but was in the UK from age of 5-17
- Based on profile, he's 20 years old, Hajin is probably 22 (second year in uni)
I'm thinking that there was some sort of baby swap that happened, but I just don't get what's the point when Yoo Hanjin just an antagonist who doesn't last long in the story.
I'm going to guess the mother cheated early on, don't know what happened to the real Hanjin.
-Busan Hanjin was picked because he matched the age and looked like the mother.
-That blonde high schooler is too young to be real Hanjin but he's probably the brother related.