"he must marry first to continue his family tree" aka he can only become a duke when he gets married and you as a child who is not considered is immediately offered to be his wife. You see him so sincerely even though you know you can't expect love on top of this contract

"Hey, at least if you know how to be shy, you have to act as a good wife in social circles. And don't try to approach me or talk to me when it's not necessary."