What is he supposed to do? His fiancee had been in coma for 12 years, she suddently wakes up with abilities that she isn't supposed to have and there are suspicions of black magic going on, of course he doesn't want a black mage wreaking chaos in her body. To me his actions are pretty reasonable, especially since he was going to war.
Sia's behavior is sometimes frustrating, but we have enough hints to guess the crown prince brainwashed her to some capacity, and treated her like an object, not the best environment to question authority and understand her rights. I think she didn't flee because she wanted to bring ml's head to the crown prince? If she runs away, she wont be likely to achieve this, especially since she wasn't able to best ml even when she was stronger.
I hope too that freya and sia aren't the same person but im pretty sure they are, I dont get why all the authors keep overusing the same boring plots until everyone gets sick of them...
I get what your saying, but that doesn't explain why he gave her a job he thought she'd be bad at and she didn't need to be locked up in the mansion, she should've been able to leave with an escort. Yeah, I'm frustrated by the fl, why is she not questioning what right the Duke has to keep her locked up like he is? Idk I just hate how she's going along with it all so smoothly and like, idk I just can't put into words why the MLS behavior makes me feel icky. Maybe it's cuz he is making her work and pushing her to work hard/well? While keeping so much from her? Idk. Like I said I can understand why he is acting the way he is but... idk

Sigh I really don't like how manipulative the Duke is being. I can understand why, sure, but that doesn't make it okay to: deceive and lie to her, force her into a job he expected she'd be bad at, keep her trapped in the manor with the equivalent of a fking dog collar. Like, why is she not questioning what right he has to keep her there any more? I get she's trying to win him over but in the same breath, she could have broken that collar like she did the first time and just left while he was away at war. And for all of this and more, I can't help but see her as completly stupid, being so dedicated to the job of the person who has treated her like shit and was her literal enemy as far as she can remember. And don't give me some bull of "she unconsciously blah blah blah" because if her unconcious can sway her that much she must not have much happening in the conscious part of her brain. -.- I really wanted to like this but the way he treats her makes me feel so icky for reasons I can't fully explain, and he dumbass decisions get harder and harder to stomach every time.
Also, I agree with everyone else about if sia and Freya are the same soul I too am going to be disappointed. So lame.