This is the difference between someone that just follows the story to a "happy ending" and one that actually tries to understand the "person" in the story.
Aeneus tried to follow a story in hopes that it would get to her happy ending with the prince. But this made her not actually like the prince for himself, but rather his position, and just this "happily ever after" ending. The result was that the smallest deviation and her own personality screwing things over that caused them to be on the rocks. Not a happy couple at all.
Meanwhile, because Triana knew about Meduon's story and efforts, she resonated with him and wanted to understand and get to know him more. Which made him fall in love with her and thus they have a good relationship. A truly happy couple.
Aeneus tried to follow a story in hopes that it would get to her happy ending with the prince. But this made her not actually like the prince for himself, but rather his position, and just this "happily ever after" ending. The result was that the smallest deviation and her own personality screwing things over that caused them to be on the rocks. Not a happy couple at all.
Meanwhile, because Triana knew about Meduon's story and efforts, she resonated with him and wanted to understand and get to know him more. Which made him fall in love with her and thus they have a good relationship. A truly happy couple.