"I only did what your father told me."
"What my father told you?" Anna responded in a mocking tone. "Heh. Do you even plan on telling me?" Anna understands if her father told Kyle to not tell her the truth, but right now, she wants to know if Kyle ever thought about telling her.
"Of course! On the day we were alone together, I wanted to tell you about it! It's not just because your father told me not to, it's also because of my selfish reason. I don't want you to feel sad on that day."
Anna deserves the truth about her father, but Kyle's selfish reason blocked that thought. He would rather see her smiling in front of him that day than to tell her the truth about and be sad in front of him.
Kyle does not regret not telling Anna the truth. More than anything, he loves to see her smiling every day. So not telling her, is a choice that will stick to his mind for the rest of his life.