Promising start but I'm not quite sold
Review written after reading 10 chapters:
Read the story now
I think that there are some really good plot elements here, but parts of it are a bit clunky for me. Sienna's character is realistic, although I agree with another comment I saw that there is a bit of a data dump in the first chapter that would be better to have the reader discover slowly or after her character is a bit better established.
Xander's character, however, isn't quite working for me. He's supposed to be some super powerful mafia boss, yet loses his mind over a girl after seeing her for two minutes? Also, how did Sienna discover who he was?
I think that the conflict between the two of them that shows up at dinner with his family would have been better if it had been put off a day or two. When they have barely known each other for an hour (at least an hour of Sienna being awake), and Sienna has made absolutely no reference to having positive feelings about him at all, it shouldn't feel like that much of a betrayal that they come from rival families.
Also, I like the idea of alternating narrators, but when you do the exact same scene from different points of view and repeat the same dialogue, it gets repetitive. I would suggest alternating time as well, or having one character just think back to what happens so you don't need to repeat everything to put a new spin on it. You can have a direct quote from Sienna, and then when Xander describes it you could say something like: "When Sienna demanded that I pay for coffee at my own shop, I couldn't believe that she would be so daring". As you expand the characters more, we don't need to hear everything from both of them, because we will be able to read past their spin and imagine what the other one of them would have thought about the events in question.
I would also keep the mantra "show don't tell" in your mind. Let the reader form their own impressions of the characters instead of describing their personalities. I feel like you do this better for Sierra than Xander.
There are also some grammar problems and typos that were interrupting the flow for me, including in the summary where I think you used "despise" instead of "despite" or vice versa.
I'm sorry if I sound harsh. I think you have a promising start here, and with some editing and expanding the chapters you already have, I think you can turn this into a really good story.