I have a feeling that Aria was forced into this and didn’t actually want to marry the hero. Mark my words, there will be an Aria redemption arc (not spoilers, just speculation)
Yeah, I think something could be up there. I'm not sure either sibling stuck around there long enough to see things all the way to the end. Perhaps the next day, the capital was full of rumors about how a saint had delivered an epic beatdown on the so called hero in front of the king and everybody for stealing a kiss from her and demanding her hand in marriage without her opinion on the matter. He left and his sister went to chase after him before either could see it. Then he left the whole city before word could even spread.
On the other hand, it was a long journey. Sure, hero was a dick when we first saw him but we have no idea what happened on that demon king murder mission. Maybe he became a better person in the journey and she fell for him along the way. Maybe it was the damn suspension bridge effect from fighting for their lives alongside each other. Point is we don't know and neither did the MC from how this was presented. Cut and ran before he could even find out.