asami ryuichi future wife's feed

Why didn't fl tell the sister/brothers wife? Like girl do you want your brother to turn into your husband 2.0 like you saw him cheat so be a girl's girl and tell the wife especially when she was nothing but nice to you. And IF they DO divorce when it's revealed that the red/brown haired girl was a witch all along and was working for the royal family then the brother can marry his wife again or stop the divorce (if she leaves).