
I just checked and chapter 48 was chapters 102-105 of the novel, so the manga is going way faster, but the manga is following the logic of the events in the novel, so there's no way to predict for certain.
Navier's divorce happens in chapter 164 of the novel, so my prediction is around 20 chapters more to go.

As I said in another reply, the events of ch 48 happens in ch 102-105 of the novel, and the divorce started in ch 164.
However, the manga is following the logic of the events, and all these events I said happen before the divorce, so my guess is 20 more chapters to go.
I think it's important to mention that the novel chapters are divided in 2 parts (i. E. Ch 164 I request permission to remarry (1) and 165 I request permission to remarry (2)) so we can expect AT LEAST 2 novel chapters per manga chapter. So no more than 30 chapters to go.

SPOILERS
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He's gonna be mad bc his plan was to remarry her once the baby was born. He'll try to forbid it, but the High Priest will say that's under his authority and there's no way for Sovieshit to overrule it.
So he puts Navier and Heinley on house arrest (sends knights to siege her parents' house) while he tries to find a way to prevent her from marrying.
But there is no way to stop it. Only way he can do that is if he requests annulment of the divorce, and that would mean annulment of his marriage to Rashta as well, and his plan would be useless, so he can't do that as well.
Meanwhile, since Heinley is King, he can't keep him without causing a war, but he also doesn't want to release him and look weak. So he tells Elgy to "smuggle" Heinley out so he can save face, but not Navier.
Except Elgy double crosses him and smuggles Navier out as well, and Sovieshit just realizes 2 days later, when she's already gone.
He goes crazy, but nothing he can do. He'll keep pestering Navier in the future tho.

Two babies, actually.
The best part is, Sovieshit thought he or Navier could be infertile, so when Trashta got pregnant, he thought it was Navier.
However, when she gets pregnant, it becomes clear that she was NOT infertile... So it must have been him. Which means Trashta's baby is not his.
(Truth is, Navier was infertile. But Heinley's bed was magical and cured her lmao. It was uncertain if Sovieshit was also infertile, haven't reached that part yet).

Trashta is going to be executed, along with Viscount Roteschu.
Sovieshit is going to learn everything about her.
Only thing I disagreed with was that he also killed her baby daddy. I pity the guy.
I also know someone took both Trashta's babies out of the country to protect them from Sovieshit, and he goes mad bc he already loved his daughter (idk if biological tho).
Guys. The divorce is getting close (spoilers ahead of what's gotta happen before that), but given the events leading up to it, I bet it'll be at least another 15 to 30 chapters.
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Her brother is gonna find out about Rashta's other kid through shady means, and the Emperor is gonna use that as grounds to banish him.
Then, after Navier refused to adopt Rashta's baby, Sovieshit is gonna realize he's gonna need to marry Rashta to make this baby a legitimate heir.
To marry her, he's gonna make up a fake noble family for her so she can be accepted as new empress. Howevrr, Duke Elgy will get a fake family as well, just because he likes to see the world burn.
Now that there are two families, the emperor is going to use that to set her brother up and justify a divorce.
Navier is going to realize what Sovieshit is planning when she proves her brother was innocent, but he is intent on blaming the brother.
Important note is that she grew up to be empress, and she is self-aware enough to know that she doesn't know what else to do with her life if she's no longer Empress. That's when she remembers Heinley said he'd have her as queen that she decides that, if she can't be the empress of the Eastern Empire, then she's gonna be queen of the Western Kingdom.
During a visit to that mage girl she's sponsoring, she's gonna bump into Heinley and propose a political marriage, and they start planning. However, he's gonna tell her he wants an actual marriage, not a fake one, and she agrees.
That's when they start plotting through birds, and her relationship with Sovieshit starts to deteriorate as well as she basically checks out of the relationship once she realizes he's going to divorce her, not knowing that his plan is to divorce Rashta and marry Navier again once the baby is born (smo even tells him he should tell her his plan).
It'll get to the point where he starts trying to gain her favor again, but she's done with his shit and he gets angry and demands any birds flying to her window to get shot down, as he realizes she's getting letters.
At the same time, there'll be a plot about Rashta realizing he's favoring the Empress again, getting mad, and plotting against Navier. Also a plot between Rashta and a maid (important for the future).
Then there's going to be a plot about her trying to find new means to inform him of the day of the divorce so he can be there to request remarriage, as both parts have to be there to make the request. She's gonna talk to him through Duke Elgy and/or Marquis Farang (the guy we see protesting the divorce in ch 1).
Then the High Priest is going to show up after Sovieshit requests him to come down, he'll declare his intention to divorce her in the Chamber of Lords. Then she has to find a way to warn Heinley that Sovieshit made his move before she's locked up in a tower, per custom before divorces, so he can be there in the day of the official divorce.
Meanwhile, Navier manages to get the Priest on her side, as he is unhappy with Sovieshit bc he requested divorce bc of infidelity with Rashta (the priest interviews with each divorcee before the official day).
Another side plot of Elgy pretending to be Rashta's friend just to sabotage her.
Heinley gets there the night before, and JUST THEN we have the divorce.