I don't know much, but some said in the comments that he's really sick
Waaaaaahhh
Spoilers (?) I don't remember then correctly
But her brother is the one that turned back time so Lily could live again instead of being trapped in the tower like in her last life
Spoilers below
Based on the spoilers I read ages ago, he thinks his magic (that turns back time) is what's causing Lily's illness to get worse (and/or he thinks he's about to die from turning back time, my memory is fuzzy). He left a little before the story started, thinking that if he was gone, she'd start to get better. BUT he's wrong! His magic does not affect her. He'll pop up in the story a little later. He comes back after Liliana gets badly hurt and takes her back home to raise her.
Someone tell me about her brother