Okay... You can't compare people from two different lifes... The prince from the last life is the last life and Allendis from this life, is from this life... You MUST compare the two, using the same timeline and same life... I'm sure that Allendis from the last life would also treat her like shit... LOL
And I'm sorry... But if you want to be with a guy just because he treats you nice while plots people's muders (even your own father) behind you back, you're pretty twisted as well...
Tia would NEVER like someone who treat people like TRASH just because they treat her right... And Allendis wasn't nice... He's not nice, never was... He's a sociopath, if he gets tired of you, he'll throw you away...
You should read the novel... I'm saying that because I read the novel... Besides... As I said... The prices are different people... They're not the same...
Last life is last life and new life is new life... The only thing is that Tia has memories from her past life... It's like parallel worlds, the world may be the same, but the people in it are different...
SPOILER:
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Normally he wasn't like that... That duke I never know how to write the name used to give the prince some kind of drugs in order to distort his mind and then control it... Tia's father wasn't dead and the Prince tried to stop them from giving her the death penalty... But because he didn't have the power and the Duke was already on top of him, Tia was executed... He regretted what he did and he was even grateful to die, so he would meet Tia and apologize...
He did kind of dislike Tia in the last life, because of her mother... Although he regarded Tia's mom to be his own mother, Tia dared to bad mouth her in front of him, like her mother was nothing... Not even remembering their past together when they were kids...
The Tia from the past wasn't so nice either, she used to think that people were only to be useful, she couldn't even pay attention to her own father... Both of them too heartless and cold on the outside...
The entire tragedy was a bunch of misunderstanding made by Duke to dispose of Tia and her father, so he could control the prince and the entire country...
They did do wrong, but it's not like they meant it to happen like that, they were all used like chess pieces by that asshole of a Duke...
THANK GOD in this life Tia is better at showing herself... Because of that, even the prince is more mature and won't be controlled by that damn Duke... BUT... Jeannete... Oh Jeannete... While Tia only wanted to go back in order to fix her relationship with her father, Jeannete only wants revenge, she's vicious to the bone...
I hope the novel plays fair and show how people took advantage of Tia and the Prince's frail relationship...
The Manhwa changed a little from the novel in the beginning, they shouldn't have even showed that much from her past life until much later...
If you pay attention to the story, you'll see even Tia changed A LOT from her past self...
And that is, of course, what Tia DOESN'T know... She doesn't know what exactly happened around her... She only knows the basic of what happened... She thinks the Prince executed her father... which he never did... She thought the prince hated her, but she didn't know that he also thought she hated him and the Duke and Jieun even framed her...
AND I GOT THE NAMES MIXED... Is not Jeannete, It's Jieun... I was reading Suddenly Became a Princess One Day and now I mixed the two women's names... :v

So... I get why people are pissed off with the prince, considering the last life and all...
BUT WHY ARE PEOPLE STILL DEFENDING ALLENDIS!? How is he any different from the prince? He even planned to take her father away and strip him away of his title, so just he could ISOLATE her...
We all know that usually, guys who want to isolate the woman from everything and everyone end up killing everyone, instead of realising their wrongdoings and admiting they need to stay away... :V
From the beginning, what he had towards Tia was PURE EVIL OBSESSION!
So people... Let's not be hypocrites... If you don't want her to be with the prince, you MUST NOT ship her with Allendis... I got pissed off by people defending Allendis even though he did all that... In the manhwa only showed him doing her hair, but in the novel, Allendis imagine him raping Tia at the same time he strangles her...