Gatsby lives in West Egg right across the lake from the love of his life, Daisy. His mansion was specifically placed so that he could have a direct view of the Buchannan residence.
Gatsby's love for Daisy caused him to not ever wanted to be far away from her. Across the lake, her house was visible due to a bright green light which was seen every night by Gatsby directly from his front porch.
The green light in the story symbolizes the always possible love connection between Daisy and Jay Gatsby. This is because no matter how far apart they are love will eventually bring them back together to one another.