I liked it.
It made me cry (even though I knew what was going to happen...
Such an emotional response should be an easy 5-star, but...
The writing...
...was passable.
Several 1st person POV's, fine. But, I got really sick of the POV person telling me what another character was thinking or feeling. I'm much more of a fan of being shown the other character's body language and being left to figure it out for myself.
I wondered all the way through why we were never in Mia/Chloe's head... found out why in the Epilogue, which I found a bit of a let down--up to the Epilogue it was a (reasonably) happy ending... the Epilogue kind of ped me off (because it gave us insight into a character that spoiled the image I had of them up to that point). I don't know if that was the intention. A twist ending was the intention, clearly, but I'm not sure if it was worth it for how I went away feeling. Before then, I was reasonably happy with the end (despite my tears).
There was also a good few moments where a character was keeping things from the reader, obviously with the intention of confusing us for a bit and then going "Ha ha! THIS is what I was talking about the whole time"... Well, like many other readers, I don't like the POV character whose head I'm in deliberately keeping secrets. It's like they know I'm there...
Anyway, overall the premise is good. Overall the characters are fine. I guessed much of what would happen between them, and even knew there would be a demise of one... and still I wanted to read on for the journey. So, the plot and characters were fine. It was just the head-hopping and the Epilogue that ped me off enough to drop stars.