@Centurionzo probably something in the notebook touched him and now he realized how he can't live without her and all that stuff. Or maybe she was somehow very magical and was the reason why he never had any headache before? Anw there are plenty of reasons, we just have to wait to find out.
And he wasn't sad because he is fucking heartless. He didn't give a fuck about her when she was living, so why should he care if she died.
@zokoi19
Reminds me of "Actually, I was the Real One", but here, we start the story off by moving on from the death of the FL and seeing the aftermath.
It's rather nice to see how the emperor is starting to notice how not having the empress with him is causing so many problems. You only know what you have when you've lost it.