The duke doesn’t get along with the royal family so he avoided them most times. He can guess the prince is an ass but he’s still the prince. You don’t let people die without reasons. he only interacted 4 times with MC so ok there is some attraction but they’re not going out or anything. You don’t kill a potential crush fiancee just out of petty jealousy. He doesn’t know the prince is a cheater or tried to kill Mc and so far MC has keep a happy facade in public so there’s no way for him to know that she’s not in love with the prince yet... sooo yeah your anger is pretty misplaced
I'm angry the Duke had the opportunity to let the deer trample and kill the prince but he didn't let it happen? For what? The chance was there my guy no one else was around you could have pretended you had just arrived and was too late and the problem would have been solved