If the heroine is to fall in love with the hero (and vice versa), there's going to need to be some time together. The problem being that the hero does not want to spend that sort of time unless it's work. Especially when he realizes he's falling in love with her. (Hmm. I wonder whether he's going to realize she is, or he is, first.)
Thing is, he's courteous enough to know he can't dodge it all, when she's the king's daughter, and he's the king's knight.