tamborin00

After they went hang gliding, he said he was willing to offer her more freedom compared to other suitors.
I think she asked if he would be satisfied being monogamous for the rest of his life after marrying her (Princesses' husbands lose the right to multiple wives, and he was known to have many past partners).
I guess he assumed that she was hinting that she wouldn't be satisfied with one man for the rest of her life and she was hesitating to commit to him.
He then offered to accept her having lovers outside of their marriage and the two of them being more platonic companions.
This upset her as they had misunderstood each other - the vague, poetic way that nobles speak leaves room for interpretation.

You're right! But I thought she only turned away from his kiss on the night that she rejected him. It felt so frustrating watching that and knowing that communicating honestly (and accepting it) could have helped.
The pressure was on both of them (for him to perform as a man), but as the woman, she probably would have worried how he would receive her complaints about their situation.
The way he reacted the first time she rejected him/tried to do things differently was surprising to me. He seemed so responsible and level-headed before then. Maybe when it's just them two, he still expects her to not put her needs forward (like hierarchy stuff).
If a prequel could be possible, I'd love to see how the relationship progressed over the years (an arranged marriage that seemed to be mutually respectful but hollowed out and became resentful over time).

The kiss with the mistress made me mad! He never kissed his wife like that - all she got were cold pecks. He starved her of intimacy.

I thought he acknowledged that her being a Princess is a huge part of her. Her privilege has shaped her in ways she doesn't see. She is a highly educated woman in a time when education was extremely restricted for women. Other women of her class don't have the same liberties she does.
I thought he was saying, "Do you see how brave, strong, skilled and idealistic you are? You fought for that, even though everyone said you shouldn't. But you wouldn't have that chance if you weren't the King's first daughter. You wouldn't be able to choose your husband." (Like how her little sister was told she would be getting married to a stranger).
"Being a Princess has shaped who you are and the mountains you climbed. That doesn't degrade your efforts. I love your efforts to be yourself as a Princess".
But I'm sure he has a secret motive to be willing to give up male privilege, financial/career freedoms, and offering to allow her additional lovers. (Which I thought was sweet/sad because he might view himself as unworthy of her, and be willing to have her be with men who can help maintain her desire for freedom and love). (He fumbled there because she's a monogamous romantic, and he was focused on negotiating a business deal. Which, I think, made her think twice about what she was feeling for him. Like, would it kill him to write poetry, get on his knees and beg for her heart?)
Whenever I see her interact with the other possible love interests, it's obvious that she's comparing them to the merchant, but is hesitant to let herself fall for his calculated (hopefully not fake) charms.

She rejected him once, and he immediately cheated. No respect.

The subtitles for the site I used were confusing (they made it seem that the CPrince was scheduled to see the concubine). I didn't realise until the comments what his actions implied.
There is only one day a month for them to try for a baby. He knows the failure to impregnate her is blamed on her. He knows ignoring her is blamed on her inability to keep his attention. He knows he could have gone through the proper procedures to marry the other woman if he loved her so much (lol), while maintaining the Princess' honour as the first wife.
They don't know how to communicate with one another, but the CPrincess still fulfils her role diligently and respects him as her husband.
He intentionally humiliated the CPrincess, knowing his staff would gossip about where he went (no moment in his life is private.)
It is not natural for him to act in the way he did. He chose the way that he knew wouldn't hurt him but would hurt his wife.

I had to skip the affair bed scenes because it upset me so much. Having fun with her but is not being as warm or open with his own wife.
He is selfish. He never thought of how suffocated and humiliated the CPrincess felt having her only intimate marital moments being listened to by all their staff (who definitely gossiped about every sound) or her worth as a wife/woman being measured by her inability to become pregnant - which I believe is an issue on his side because she has a regular menstrual cycle and is physically healthy, but has never been pregnant.
I love the CPrincess' heart, patience and selflessness (and how the actress portrays her). At first, I hoped their marriage issues could be solved by communication and mutual support, but his actions have destroyed any respect she had for him.
Their relationship is, heartbreakingly, the more realistic depiction of an arranged marriage in this show.

When his mistress declined his offer to marry him, I laughed. She got divorced because she was 'too strong-willed' to be a submissive wife. The Crown Prince loved how carefree and bold she was. Why would she go back to the marital misery she left - you're not special! Hahaha!

I get the anger. I felt so disgusted by the Crown Prince's actions (and blaming his wife for it - which is very realistic).
But I think it was to show how a man's selfish actions are forgiven/normalised, but if a woman had done the same, she would face death. He disrespected her and humiliated her by making it as obvious as possible/ignoring procedures to marry another woman and preserve the Crown Princess's honour. She would have been the subject of gossip about her abilities as a wife.
This is her opportunity to get a divorce and symbolically free herself from social confines.

The Crown Prince definitely sees himself as a 'nice guy'.

I also hope the divorce is allowed. Maybe then the Crown Prince will see the error of his ways and realize how he is also a part of the problem - so much so that the Crown Princess would be willing to endure the shame (in this society) of divorce.
She seems very selfless and I think the Crown Prince treating her so coldly (after her best friend who lived the same life as her died so terribly) would break her last will to continue serving other people over herself. She must think, "If I don't leave now, that will be me. My life will always belong to everyone else if I stay."

I don't think he will. His affair feels more like punishing/blaming his wife rather than breaking free from the system that makes him unhappy. He could have brought his discomfort up with his wife/parents to make the process easier for both he and his wife.
What true life story is this arc based on?

The romantic music pissed me off so bad. Maybe the intention was to show how the two of them/or just the CP think the affair is romantic or based on love - even though it happened very quickly and immediately after the CPs conflict with his wife? (Like the air is sweeter/ freer outside the palace.) Because similar scenes with the Crown Princess are monitored by staff and are uncomfortably quiet.

It was quite clear from the beginning that this universe isn't rigidly accurate to how the records from the Joseon dynasty are. I don't understand why some are saying it's too Westernized. Is it so crazy to imagine that people in the past are so similar to how we are now?

The Crown Prince knows there's a process to introduce a concubine into the palace, and it's up to the Crown Princess (and I think the elders) to consent to that. He's spiteful after her denying him and chooses to lie and cheat when he could have asked permission to take on another concubine.

The site I use has good quality, but the subs aren't great, and only the first 4 episodes can be viewed.

Can I ask what contemporary references you noticed?