Dominion. The Serenity Series, #4

The ultimate sacrafice for eternal love... Since meeting Serenity eight years ago, vampire Sebastian Bandores' whole existence has been about protecting his family. But when an unexpected question causes a rift between the unlikely couple, Sebastian finds himself with a dead body and no recollection of killing him. Serenity sees something dark in Sebastian's face and feels as though she's being haunted, both by her inability to let go of her past and by things happening in the house.
When Sebastian's strengths start to fail him, the couple seek help from a friend they're unsure they can trust. As Sebastian loses his grip on the real world, Serenity fears they may be too late. And after everything they'd been through during the past eight years, Sebastian never imagined he'd be the one who'd need saving.