Deep sigh it seem i have to be the only rational asshat in the comment section.
So far the story made it clear the demon are the aggressor and clearly seem winning, The human have the right to be angry, downright hate the demon for invading their homes and killing.
The hero is understandably hate the demon more so the demon princess.
The demon princess genuinely love the hero and wants to be close to be said hero.
HOWEVER, being a jackass, especially to your fiancee is not a smart move. Like hell, do even heard being civil? Being formal? have a courtesy? No, i guess not.
Look, i'm looking you two being lovey dovey from the get go, atleast being respectful atleast a formal kindness? I'm fine you hate the fella but clear boundaries of respectful as your partner and common decency.
Let's look in history, You got two warring nations, then one of em asked for ceasefire, to reinforce the ceasefire and peace, they send their children as a political hostage to reinforce the peace by marriage. For argument sake let's just say they're adults.
They're fine to be hate each other at the same time for the sake of peace, they have to be respectful as partner.
REGARDLESS of hating each other guts, atleast being respectful each other as a human being or atleast have some decency.
The problem is currently, the hero basically did none of that, The demon princess actively want to get close and understand the hero. There's a one sided communication and that being a hero.