My Soul to Keep by Tananrive Due
When Jessica marries David, he is everything she wants in a family man: brilliant, attentive, ever youthful. Yet she still feels something about him is just out of reach. Soon, as people close to Jessica begin to meet violent, mysterious deaths, David makes an unimaginable confession: More than 400 years ago, he and other members of an Ethiopian sect traded their humanity so they would never die, a secret he must protect at any cost. Now, his immortal brethren have decided David must return and leave his family in Miami. Instead, David vows to invoke a forbidden ritual to keep Jessica and his daughter with him forever.