
What's the reason for them to ghost him? he's so pure and innocent

According to some spoilers, his mother was receiving disturbing gifts at her bedroom door and thought it was Karhan. She confronted him about it but he denied ever doing such thing and she didn't believe him at all. That caused heavy tension in the house and animosity.
Even more spoiler ....
It was his brother that did such things and his mother, knowing she was deeply in the wrong for how she treated his youngest baby, decided to leave quietly after apologizing (if I recall correctly) and went to another mansion either in the countryside or South. She knows what she did left a permanent stain on the mother-son relationship, so gave her blessing to the couple and rights as heir before leaving as well.
what if the golden eyes actually doesn't really care about the red hair but he's just using the red hair just to reunite with his brother or cousin or whatever bc he cares about bihwan more than the red hair but bihwan care abt seoho more than the golden eyes and thats why all those thing happen in the past and only now he unsealed bihwan just to reunite
this is just MY theory alright,, dont attack me :)