Responses
Makes sense.
Facts for me: she knows about her death for several resurrections (unless the translation was wrong, this is something they mentioned at the start).
Opinions: Arabelle wasn't his lover but his sister arwin has two hearts because, as you said, one was lost to the lady who died, and now he has another for the maid.
The concept of hearts could be sacrifices of organs as you said, because of the explanations until now and the dream of the FL.
Looks nice. Totally follow.
So here's what I think is happening. I think it's some sort of situation where history is repeating itself. Arabelle must have fallen in love with Arwin, but was dying. Dalton must've truly loved her, too, to the point of keeping her body from decaying.
Now, the two men, almost against their wills, fell for the maid, Ipo. That's why Arwin said he was giving her his second heart. He had given his first to Arabelle, and thus lost it when she passed. Now they both know she is dying, and everything is repeating again. I think when Dalton realized that, it's what caused the storm at the ball.
I think the dream Ipo had was just her intuition telling her how Dalton's grief and jealousy has turned into murderous hatred for Arwin. It could be neither man truly loves Ipo, she just reminds them very strongly of Arabelle. And they do care enough to feel sorry for her.
For Ipo, that's enough, or she thinks it has to be, but I think this animosity or rivalry or whatever it is between Arwin and Dalton has been smoldering under the surface for far too long, and Ipo is what's causing it to finally erupt.