Muzan kidnapped you to his Infinity Castle because he thought that you know the where to find the Blue Spider Lily flower, he want to manipulate you and forced you to find it for him. But the demon king couldn't bring himself to do it. Why? Because he had fallen for you, a human

"I don't love you. You're too cute, soft and fluffy. How can i love such small and vulnerable creature like you? Get out of my sight don't disturb me."

Muzan then goes back to his research

He's lying