Pretty sure they met when they were kids I believe
They met each other as childern and he fell in love with her then. there was a flashback about that. Probably around the time Litia talked about the deaths of the other characters.
Oh, then when she entered the palace is that when the other characters begin to like her too? I kinda forgot about the original plot line.
When she came to the capital the main story of the novel starts. Like stories usually go, she will meet one after the other while being with the prince. And his jealousy and Ariels stupidity will get everyone killed - that's the gist of the plot.
Did the crown prince reborn or did he already meet Ariel a long time ago?