So many are hating on the female lead. I mean I'm kinda frustrated too but I can't really blame her. The whole time she never intended to be in love with Cesar because she knows he'll end up with Gracie, the real heroine. What happened with the real Canaria was also quite tragic so it's understandable that she wants to play safe if she wanted to live.
And even if she knows now that Gracie didn't marry Cesar for love, there's pressure coming from the emperor. The emperor stresses for them to get divorced and that Cesar should marry Gracie. If she goes against the emperor, things wouldn't go so well.