I don't think he realises that reading the letter affected her. He thinks nothing of it and assumes she would have too.
his butler dude straight out tells him she started acting weird after reading the letter yet he doesnt know it effected her yet?
? The butler told him she was acting weird because she wanted to know what the letters said. He's not had any interaction that we've seen with the butler after she read the letter...
He should've been happy to find the she is jealous of the girl who sent him the love letter.
dude dont go sneaking around her back, just ask her what she thinks of the damn letter (╬￣皿￣) why u gotta complicate things, eh??