The most beautiful part of telling the truth was not having to remember one's lies. To have the truth was to have freedom.
Leonor couldn't keep track of her lies and she certainly didn't feel free. She began loving someone and it was the most hurt she had ever been, realizing she had to turn against one to choose the other.
She did not want to stop loving Valerio but he was becoming more of a concept than a palpable person. On the other hand, the duke was very real and he was within her grasp.
To finally acknowledge her love for him felt like following the light at the end of a tunnel. Except following that light meant she had to leave behind the dying body of someone she did love too.
How her heart chose two people was unfair, but to keep getting close to the duke and never acknowledge the possibility of feelings wasn't fair to her heart either. It wasn't fair to the duke's heart if he felt the same for her as well.