Because Patrizia pity and sympathetic towards Lucio, he thought the empress might be as well towards Rose lol. Yeah the emperor is stupid af... But he's doing it because he's still emotionally dependent on Rose. Losing someone that he depended upon for his trauma is something he'd like to avoid but... He'll get better soon. He will rid his attachment and dependency towards Rose and will try to fix his shit(healing himself) when that happens.

I can't hate her rigth now but still i don't like her. Her past doesnt justify her currently actions.
Do the emperor think that her past will make the emperess better ? Is he trying to use it as an excuse to why the emperess have been going ? Is he dumb ? I mean, he don't have the right to talk about Rosamond past just because he feel like it especially to someone she dont like.