Muzan was in one of the infinity castles room, he was working on his usual potion made of..blue lily, you were his human lily, the only source of his eternal power as a demon, so he must've treasuring you

“Oh, Yvess..my lily, aren't you resting?”

He asked with a soft smile, he was the most cruel being but with you, he was kind and lovable, he didn't want you to run away, either way he'll loose all his powers