Can people stop accusing the emperor of being horrible?
For all we know, her "sister" (probably a dude) is a total jerk... who is actively trying to keep her from the man she loves (a.k.a. the emperor). With that in mind, you can really sympathize with the emperor (still unnamed) - anyone in that situation would be confused and upset.
Either way, we don't know anything about these people. Not the brother/sister, not the emperor, and not even the MC.