Flames of Lethe by Lexie Talionis

A land of eternal youth. No death, disease, or decay. But this is no paradise. And no one here is an angel. Jo and Christopher awaken naked in a desolate land where memories have vanished. Horrified by their new reality, Jo wants nothing more than to lean on her beautiful, fiercely intelligent companion—until she sees the contempt in his eyes.
Christopher, rational and controlled, wants Jo to keep her distance, especially when he has such a hard time controlling his body whenever she is near. And stranded together without anything to use for clothing, his control is slipping. It is only a matter of time before the fire building between them consumes them both.
But forgotten sins simmer beneath the surface, and the underground shelter they find at last becomes a prison that threatens to tear them apart forever. When a powerful man from their past emerges to claim Jo for his own, reminding her of a love from a time gone by, she must determine what is real and ultimately fight the entire world if she is to hold on to the love that has only just begun to burn.
Yet in a world ready to punish them at every turn, what chance does love have? Hell is no place to follow your heart.