Gatsby waiting to make sure Daisy is okay outside her house.
In this scene specifically Tom, Jordan, and Nick are outside of George Wilson's shop and he isn't looking very well. George tells us that Myrtle is locked up in the room upstairs and we learn that she is looking enviously at Jordan thinking that she is Tom's wife Daisy. Although no one seems to notice this she takes note of the car and continues to stare angrily at Jordan as George tells us that he and Myrtle are planning to move west.
In this scene we are at the end of chapter 7 and this is after the Murder of Myrtle. Daisy and Gatsby had returned to Daisy's home. Daisy had told Gatsby that she would flicker the lights if Tom was hurting her for hitting Myrtle, however she never needed to flicker the lights. Although she did not flicker the lights Gatsby still waited and watched from behind the bushes out front where Nick had found him on his way out to the street in order to catch his cab home.