Jenna/Zena's plans are in motion and he wants even more power, so he begins to poison Ruve with a psychotropic drug that makes him angry, bipolar, and schizophrenic.

That's in part, the reason why Ruve speak harshly to Tia and is harsh in is behavior, but it's mostly because he is broken cause he think she can't stand being with him. In fact, it would be more correct to say that he is desesperate by that.

Jenna also feeds lies to Ruve and Ruve hears the people and staff... basically everyone saying how Tia is a total smug, superior b***h who is power-hungry and pissed off her plans to get power failed cause Ji-Eun showed up.

There are rumors that Tia wants to assassinate Ji-Eun so she can get back the place of Empress.

Ruve confronts Tia and wants her to be honest with him, but she basically thinks "I'm scared of you, I cannot be honest with you" and tells him "you won't believe me anyway" and Ruve goes "So you're basically admitting all the rumors about you are true."

Now don't forget he is drugged with those psychotropic drugs FOR YEARS, so that's when he rapes her. And of course, later when he pushes her and causes her to miscarry.

But Ruve is fed by Jenna's lies and he is persuaded that Tia is power-hungry and and feelingless. It's Tia who take of her clothes by herself and it's clearly writen in the book : Ruve wouldn't have done anything Tia didn't wished for. But he is persuaded that Tia want to conceive the heir so that she can get more power. He his so desesperate that he think it's okay for him to be only a breeder in her eyes since in that way he will be able to be by her side.

So he does feel extremely guilty about raping her, but it's explained that he couldn't control himself because of the drug added somehow to his feeling for Tia. (I don't understand this part either, don't ask me.)

I am not trying to defend him, because rape is something unforgivable whatever the reasons are, but it's explained that in a way he wanted to convey his feelings for Tia (ugh?) and it's stated in his POV that he didn't wanted to rapes, her he wanted to make love to her.

In fact, if we look closely to the matter Tia was somehow in the same state of mind, remember she think: "If I conceived his child, mabye he will look at me once again."

When Ruve learn at the banquet that Tia is pregnant he is really overhelmed with pure elation and glee and his very first reaction is to want to take Tia in his arms. He didn't because of Jieun.

He consider the fact that it may not be his child but he doesn't care and he swear to himself that he will give this child love because this is the child of the woman he love.

After earing the news, he really wish to go to Tia but Jieun prevent it. And the three weeks later when he finally get to see Tia he is upset because she won't even smile at him.

Tia just tried to be respectful but she seem cold in his eyes.

So he tell her those horrible thing : "you're children will never be my heir" (keep in mind that he is still under the influence of the drug and that he didn't mean it).

While in fact, he think the exact opposite. -_-

Then, Tia collapse because she is druged too and naturally frail, added to the fact she have to do all the empress duty (Ruve doesn't know that, he discover it after she died and feel guilty about it).

So, Tia collapse and Ruve catch her but then Jieun enters and Tia miscarry.

We don't get to see it at first because it was written from Tia's POV but Ruve carried her and stayed by her side until he learnt she miscarry and that she can't have children anymore...

But when Tia finds out she miscarried and can no longer have children (her womb is damaged), she laughs crazily in despair in front of many maids/servants, basically cursing god (Vita) for her life.

We don't get to see all that since the novel is written from Tia's point of view, so it's subjective.

They are both lock up into their view of the situation and they doesn't even know how to comunicate with each other anymore.

It is also clear that the palace staff is also to blame for Ruve's perception of Tia. They were really malicious in their gossips and reports to Ruve. For example when Tia loses her child, Ruve is deeply hurt too and wants to reach out to Tia. To see if he can somehow create a bond with her, now that she might suffer like he does.

He somehow hopes that she developped feelings at the death of their child and he could comfort her and connect with her. But the palace staff report to him that Tia laughed at the news of her miscarriage (while she laughed in despair because she heard that Jieun was pregnant and she was barren - what a bunch of liars), and 1st Ruve is so angry and hurt that he curse Tia for her cruelty and breaks things in his office.

Zena and the palace staff report that Tia laughed like crazy, saying "I'm so glad I don't have to give birth to that f**ker's baby. Thank god I had a miscarriage". Of course Ruve gets pissed off at this and thinks what kind of monster is happy her baby died. Thus Tia just confirmed all the rumors about her.

So once again, he had regained a bit of his sanity only to lose it again.

Tia's father, Keiran, understands Tia is unhappy and miserable and begs Ruve to take Tia away. He wants to fake her death and have her live quietly in another country.

At the same time, Zena fakes an assassination on the pregnant Ji-Eun and blames Tia for it, but Ruve has some moments of clarity. He thinks "If Tia wants to escape to another country, why would she risk killing Ji-Eun? The only point in killing Ji-Eun is if Tia wants to stay and become Empress."

I'm kind of confused too with the novel/webtoon, but I think there's not enough evidence to tie Tia + Keiran + her house into the assassination attempt, but Ruve & Tia fight and he lies to her that he killed her father, because he wants to hurt her in retaliation for her laughing that their unborn child died. Tia, who was also poisoned by Duke Zena, goes crazy upon hearing her father was killed and stabs Ruve.

Tia wounds Ruve in a fit of rage, and it's obvious she doesn't understand how she could have done this. Knowing Tia, it's also hard to believe she could do that, even to her worst ennemy. It's because she was also poisoned with the same poison Ruve had been fed.

I mentionned that fact when she got angry at Jieun, but in the manhwa you can clearly see that on the morning of the stabbing she was completely unable to sleep the night before, so the poisoning is getting worse. Her stabbing Ruve was actually also Duke Jenna's will and doing in a way. Both her and Ruve were not in their right minds and not the masters of their destinies anymore.

Of course, now there is enough evidence that Tia committed treason, attempted assassination of the Emperor, so Zena and everyone votes to have her executed.

Ruve actually votes against them but is outvoted. We know that Keirean wasn't killed by Ruve in 1st timeline because he's present at Tia's trial. And Ruve is shocked to see that Keirean is not defending Tia. He was planning to use Keirean's defense to save Tia, supporting his defense against the nobles' faction.

But with Keirean staying silent, Ruve is trapped and cannot get Tia a lighter sentence. (Actually Keirean had another way to save Tia because the Monique family have an imunity this is also the reason why Ruve's father didn't forced Tia into the marriage.)

This is my speculation but Keirean staying silent is maybe it's because of the Monique's oath?

Because Tia's execution was the emperor's order, I think Keirean could not defend his daughter. Even if he wanted to, with how much Tia seemed to be unloved by Ruve, there's no guarantee Ruve would pardon Tia even if Keirean risk his life by violating his oath. He might chose to get revenge for Tia by himself, that's why he chose to keep his life and not to defend Tia at that time.

If that's true, then that would be very sad. I weep for Keirean in 1st timeline. I can't imagine how he feels when he attended Tia's execution. He's unable to protect his wife whom he loves dearly, and then he also could not protect their own daughter.

Anyway Ruve only wants Tia banished so she can live happy in another country. He was actually trying to grant her wish to escape the palace.

However, Tia is executed and dies thinking Ruve had killed her father and sentenced her to death when none of that actually happened.