you are kinda valid bcs i remember jin saying smthing like how jitae's face makes him want to vomit. there is some resentment here and it might be related to jitae's father.
Tbh, I think the fact that Ji-an isn’t Jitae’s father’s child serves as proof of his father’s loyalty to his wife, and that he was likely set up (???). So if it turns out that Jin is an illegitimate child, it would feel quite strange. Not to mention, Jin is the same age as Jitae, and Ji-an’s mother alone was already enough trauma for him, let alone involving another woman.
But maybe they’re relatives(?) cousin perhaps?
Either way, after finding out Ji-an has no connection to the Baek family, I feel like nothing would be too surprising anymore.
Now that Jian is for sure not related by blood to Jitae, I can finally express my theory about Jin.
I had this feeling that it was Jin that is actually related to Jitae. It would very much explain the hated he has for Jitae's family. What if he was the illegitimate son of Jitae's father? Or something happened to his mom too that lead to this revenge? And look at the both Jitae and Jin? Aren't they like...very similar, albeit Jin looked ruggedly handsome and Jitae is the clean cut handsome type? Idk if the author intended for them to look similar though for artistic purposes or it is a subtle reference to a future revelation of Jin's birth parents.
I'll have to wait for the future chapters. I love it when the plot is very creative and has a lot of twists!