Series information from Goodreads.

"One cold, crisp night, Jack Sommers was faced with a choice--live forever according to the ancient, magical rules of Gaia, or die. Jack chose to live, and in exchange, he became a Winter. Like the other Seasons, each year Jack must hunt and kill the one before him. Gaia's rules are pretty straightforward. Winter kills Autumn. Autumn kills Summer. Summer kills Spring. And Spring kills Winter. Which means that Jack kills Amber. Amber kills Julio. Julio kills Fleur. And Fleur kills Jack. They die. They train. They hunt. But when jack and Fleur--Winter and Spring--fall for each other against all odds, the true brutality of their eternal lives becomes all to personal and all too painful. And Fleur is on the brink of being Purged, forever. Unless they can come up with a plan to stop the cycle. When the four Seasons unite, risking immortality for a chance at love and to reclaim their free will, their cross-country escape brings them to a place where they must defend each other against a creator who seeks to destroy them."--Inside front jacket flap.