Spoilers!

Spoilers!









No really...















OGRuve was drugged and groomed by Zena to hate Tia since he was very young. Add on serious mommy/inferiority issues and you get Prince Shit Ruve. But even then he was seriously in love with Tia. Just more of a "I hate you for being too awesome and dazzling" sort of thing. He was genuinely happy when she got pregnant (after he raped her, ugh). He did not cause the miscarriage! She was drugged by Zena and the fall was just incidental. After he found her laughing manically after she heard the baby died, he thought she was happy it died. Which bred even more resentment. So he told her he had her father killed for being disloyal. He wanted her to feel the pain of losing a loved one. Note here: her father was not actually dead at that time, but still preparing for Tia's escape. But she went and stabbed him (justifiably) when she heard this, which became a point of no return. The other nobles called for her execution, lead by Zena. That's when her father actually rebelled and died.
Things were starting to spiral out of control for Shit Ruve. He just lost his most loyal knight and was about to lose the woman he both loved and despised due to his own error, a lie that fell from his lips to hurt her.
In the end, Shit Ruve nearly stopped her execution. He was just a second too late. His hesitancy became his lasting regret and soured his relationship with Zena, Jeiun and the rest of the nobles, even the ones on his side. Add on Jeiun's incompetence as a monarch and Zena's interference, drugs, etc... and things go to shit fast for Shit Ruve. In the end, he's driven out of the monarchy and killed. And Jeiun soon after now that her use as a puppet is gone.

New Ruve realised, with Tia's change in attitude, much much earlier that Zena was full of shit about Tia and probably about a bunch of other things and distanced himself from Zena. With him out of the way, and small nudges from Tia when they were young, he was able to resolve a lot of his personality issues and inner conflicts. He is not the same guy as Shit Ruve. He reacts differently, had a better relationship with his father, not addicted to drugs and isn't surrounded by toxic people in his inner circle to influence his judgement. The muck was cleared from his eyes and he could love Tia in a healthy manner. Without all the old resentments, jealousy and lies between them.
To the point where Jeiun, or any other woman, doesn't even appear in his eyes. There's only Tia.
Now Tia only needs to resolve her own inner conflicts. She says she loved him when he was Shit Ruve, at his worst, despite everything. Can she love him at his best? And it's not like this is Jeckle and Hyde. He won't suddenly turn into Shit Ruve. He has grown up to be a good stable man. She only has to dare to love again to get what she wants(?).