In Still Darkness by Dianne Duvall

In Dianne Duvall s world of Immortal Guardians, the stakes for mortals are high, but the cost especially to the heart might be higher ”

It s not the first time Immortal Guardian Richart d Alencon has saved a human life from eternal damnation. Usually, he moves on, a nameless savior like a ghost in the night. But this time he can t seem to forget the woman who rewarded him with a sensuous kiss after he rescued her from a trio of vampires. While Richart knows that loving a human can only bring trouble, the taste of forbidden lust is too great to resist

Jenna never imagined she d end up a single mom working overtime to put her son through school. But she might have daydreamed once that a devastatingly gorgeous Frenchman would sweep her off her feet. Now that a package of tall, dark, and handsome seems intent on doing just that, doctors are telling her she may not have long to live. But Richart is telling her just the opposite. All she has to do is abandon her humanity.