Responses
Seems also that part of the cause the brother and the advisor had to pay back the karma and keep going with their memories intact is the pain and suffering they caused Hyoun, and the dragon's power or his being backed up by the heavens cursed them to pay back the karma and not be happy while still living
Just as Hyoun was while waiting for Taehyuk to come back
Taking into account that Taehyuk took so long to reincarnate and he just got his memories back like a week ago, it makes sense that he cant forgive the brother just yet.
The brother suffered a lot to pay back for his karma, maybe Taehyuk being alive again is part of a signal he has repaid his debt and now seeing Taehyuk happy, the brother can now be free.
Ofc with Taehyuk just recovering his memories everything must still feel fresh and he must feel a bit guilty for letting Hyoun suffer on his own for those centuries, and also resent not being able to be happy as he was persecuted by his brother his whole past life and he also caused his death and the death of members of his family.
Maybe in a few years Taehyuk can look back and rekindle his relationship with him on his own terms