Tragic Fire Vagina Murders Crown Prince

I'm not sure what type of novel this was, whether it was romance or fantasy, but it was intense.

I don't remember a lot about it. I read it was I was about 8 and I really shouldn't have. (This would have been in the 2002-2007 range. Though the book was not a new one at the time I don't think)

I remember the main character was really sad and it kept flipping POV between her and the prince of this fantasy land (and I think a third girl?)

The MC ended up getting captured and became a slave for the royals and the prince took a liking to her. He was supposed to be married to the third girl and she was stressed af about this (because there was a lot of shit about being a Proper Virgin for the prince) the queen was happy with the third girl because it was a powerful alliance.

The prince ended up running away from the castle, taking the slave girl with him. He knew that he and the slave girl were siblings I think? I could be wrong about that one. They eventually take refuge in a cave and one thing leads to another and they start getting hot and heavy (which was uncomfortable for a multitude of reasons) and slave girl is a Virgin and is experiencing so many new things and as she climaxes her fire powers incinerate the prince.

Fucked up right? (8yo me was traumatized. It really drove home the No Sex Before Marriage thing.)

So she kills her lover/prince/(brother?) and now has ballin fire powers but is on the run from the castle.

They may think she kidnapped him but idk

Everything was based off of India I think?

Thank you!

EDIT: I'm 87% sure the cover was red

EDIT 2: I think there might have been a servant who helped them escape? He waited outside the cave but I think he died too.

EDIT 3: I think it was part of a series, almost positively the first book, but I'm certain there was at least a sequel