"Why wouldn't you travel by main roads?"

Eist (& Calanthe)

As media has so extensively shown us, there are very, very many potential pitfalls when portraying a relationship. When people bring up what's nice about this one, they often say that Eist actually likes Calanthe, and while that is definitely a thing you want, that alone isn't enough.

When we're first introduced to Eist, he's playing Fun Parent with Ciri while Calanthe is serious. It's kind of your typical sitcom setup of Competent Woman and Dumbass Husband. But, like Calanthe, his introduction isn't really how he is, and as soon as he's not making smalltalk with Ciri and is actually talking to his wife, he's far more serious. In fact, he's the one fretting about the army's approach and ill omens while Calanthe says it'll be fine. This could have veered into Eist actually knowing war while Calanthe just isn't good enough at it, but that too is avoided as he doesn't actually advise Calanthe to do anything differently. The discussion is entirely about emotional responses - Eist is being more emotional, and he turns out to have been right to be worried, which is an unusual way to frame things to start with, and also at no point would Eist being in charge have actually changed things, since they agree on the concrete things.

At the chronological earliest point in the series, Mousesack explains the situation between the two as, "Queen Calanthe refused his proposal three times after King Roegner died, despite the two of them gliding around each other like courting swans."

What we're told is that there's mutual interest between the two. Not only that, but specifically the metaphor chosen is swans, where the behavior looks the same on both sides. This is really, really important when it's a plotline about a man pursuing a woman who's repeatedly said no. There's a lot of animals where courting is the male displaying at the female and her remaining in the vicinity is considered reciprocation, but swan courting involves mirroring each other's displays and synchronizing their motions.

And we're told this over Eist showing off how good he is with daggers, while Calanthe will shortly swagger in covered in bloodsplatter.

Mousesack adds there's a specific reason Calanthe refuses, that "She was not for living in her husband's shadow again." So it's more than just your usual strong woman doesn't want to admit to an emotion. She's refusing the marriage because it makes sense to.

As I referenced in the previous metas, Eist may be trying to indicate he doesn't have any intention of overshadowing her by loudly telling everyone about how she's very amazing ("It would have been your blade at Filavandrel's throat had you been there, Your Majesty. Not that any elven bastard would crawl from their lair to meet you on the field."). This is absolutely something Calanthe appreciates - she smiles, he grins back. That part is fine. But it's not working to change her mind about actually getting married and honestly, Calanthe would be right to distrust it. "Lioness of Cintra" seems like a title she's had for quite some time and we know everyone was amazed by her first battlefield victory at thirteen. That evidently didn't keep her out of her husband's shadow once they were actually married despite, as I keep mentioning, how we have heard absolutely nothing to suggest he accomplished anything at all.

Eist is still on her side when she starts picking a fight with Mystery Knight.

Calanthe: "A knight...of no renown...from a backwater hamlet...who dares to enter my court without revealing his face?"
Duny: "I apologize, Your Majesty. A knight's oath prevents me from revealing my face until the sounding of the twelfth bell."
Eist: "Bollocks to that."

Now, Geralt is giving her a suspicious look the entire time. He can tell something's up. Eist actually knows Calanthe, so it seems extremely likely Eist can also tell something's up, and even the viewers, who barely know her, can see there's a difference between how she cheerily mocks the previous suitor and how she's actually upset about this, despite the fact this knight should be an even safer target. It's possible Eist is acting just because he's also invested in the wedding happening, but he knows the plan's already set and nothing about some minor knight or the way Calanthe clearly loathes the guy should be a threat to that. It's very unlikely he's acting because this pings as any sort of threat on his end.