Fallen discussion

I read this book a long time ago and have since forgot the name and author. The plot circles around a fmc who meets this group of people who she knows, but she can't remember how she knows them. She ends up finding out that she and the mmc are "immortal" in some way and that she had died some number of years ago and has been reborn. She and the mmc are tied together through some sort of power, I can't remember specifically what it was. At the end of the book, the mmc ends up sacrificing himself at the end and the fmc finds him after he has been reborn so she can be with him again. It had a bit of spice, so I don't think it was YA. It was part of a series and ended on a cliffhanger. Any ideas would be much appreciated!! Most closely related is the Fallen series, but the book I am searching for is not apart of this series.

Is it called Hush Hush?

Could it be Elixer by Hilary Duff?