I was so excited for the firefighter but WHY GRAYSON😭😭

Because it had been always planned like this. You can find X ( twitter) posts of the author from several years ago. That pairing was set in stone. While of the other planned stories the auhtor only gave one name or no name at all, Desire me if you can was always Grayson x Dane. And the author also spoiled that Dane is a dominant omega. It also came up here on mangago, while the main story of Kiss me liar was still uploaded.