From The Light (Heliotropic, #1)

Serving an unjust sentence, vampire Val Cutter spots a gorgeous stranger. Contrary to his usual caution, he quickly falls for Paul de lAstre. Paul, a prisoner subjected to cruel experiments, wants only to return to his planet -- until he meets Val. But Val could never survive on sun-worshipping Apollex, and Paul will die if his sunlight deprivation continues. Forced to hide from the villain persecuting them, the men face the ultimate test of their love. With Paul dying, Val must choose for his lover: transformation and permanent exile -- or death?