Sorcerer's Feud — Katharine Kerr

Art student Maya Cayescu has always had secrets to keep--her mysterious disease that has turned her into something like a vampire, her father's obsession with ritual magic, her own talents for the occult. Now, however, she has a secret far more dangerous than those: in self-defense, she killed a man with magic. Can her lover, the wealthy, powerful runemaster Tor Thorlaksson, protect her from the consequences? He has dangers of his own to face, because his family's evil past haunts him. Worst of all, a powerful spirit from the mists of time is hunting Tor down, in hopes of taking him away from Maya and making him her own--forever.