Light is a human and Light dies,
so Ryuk resurrects him.
Kira is a Shinigami and Kira still dies,
so Ryuk resurrects him again and tells him:
"Kid, ya really ought to get your act together. Stop dying for something as foolish as love."
And Kira may be a Shinigami and Light may have been a human,
but his heart is his heart and the one thing that will never die is his love for L Lawliet.