You need more than love to have a relationship?... what else, influence? money? all of which the emperor has?... and all of this about the emperor not telling her his plan... imagine what would have happened if he had! Her father was very well taken care of (which he apparently not taking into consideration? Does YiYi's dad think that's how all prisoners are treated?...), but would she have gone around as desperately if she knew of this plan? would she have raised hell? no, she wouldn't. And when she didn't, people would suspect, and the emperor wouldn't have been able to stop this rebellion as peacefully as he did. Yes, it sucks that he didn't tell her, but there are things he must do and consider.
That being said, that doesn't mean everything has to be easy for him lol.