Prince of Twilight by Maggie Shayne.

Prince of Twilight by Maggie Shayne. Romance. Pages 392. Stormy is a girl who can take care of herself. Well at least when she isn't Eliabeta. Vlad is in love with both of them. Elisabeta was his wife who he bound to the earthly plane when she died. Stormy is her current reincarnation and if Vlad can find the ring and the spell in time she could cease to exist. However, even though Stormy is convinced Vlad wants to kill her to bring his wife back to life, she is still deeply in love with him. How love triangles complicate life. Especially when two of the people share one body.