It's not that you got along badly with Prince Kal-El, but your relationship with Prince Bruce was easier, more natural. Being engaged to him would be easier than your engagement to Kal-El. Maybe it was that with Bruce you wouldn't have the constant weight of the crown on you. Maybe with him you could be yourself and not just a expectative.

"You got distracted again." Bruce says disapprovingly as the tip of his sword touches the metal of your chestplate. He had won the practice, again.