So, my guess is crown prince knew about the pregnancy and chose his bride from the empress' side. He also doesn't trust Luce yet, considering his blood ties, and messing with him to probe what kind of reactions it will cause. He may appear as a brat but he us calculating his actions so far, not just being a spiteful, rage baiting kid. At least I'll go with that for now.
If they don't get a happy ending, neither do I.