Evermore — C.J. Archer

When ghosts begin to disappear from the Otherworld, Emily Chambers and her friends must hunt down those responsible before every last spirit, including Jacob Beaufort, is destroyed and Emily's livelihood along with them. But there is one thing stopping them - Jacob's killer. Weakened and fading fast, the ghost of Jacob Beaufort is determined to save Emily from a bleak and uncertain future. With her family facing financial ruin and the Otherworld in chaos, he knows her only hope is to wed Theo. As lives and afterlives hang in the balance, Emily is forced to make the ultimate sacrifice, or lose everything she loves.