A lonely star is a star that is extremely lonely and doesn't have anyone to talk to. It may look pretty and shimmer in the sky, but it's alone. It is also a name for a star that can only be seen in the night sky.
In the song "Lonely Star," singer and rapper ggdd refers to himself as a lonely star. He was a lone star in his life and has been for a long time but has now found someone that makes him feel like he has something to live for again.
This song was a transition for ggdd since the first version of this song was about his fans and he was singing about them all together and calling them his "body". He changed this to "star" because he now wants to sing to one person instead of a group of people.
The chorus of this song has a pulsing beat that feels as if it is a heartbeat and the background instrumentals are a constant noise that can be heard as a piercing sound that reminds you of the shimmering stars in the sky. They are very reminiscent of the shimmering stars in children's songs that you hear in cartoons and movies.
This is a great song for ggdd because it shows him as a star and being there for his fans, regardless of whether they support him or not. The lyrics in the chorus are very personal for ggdd and I believe he is telling a story about his fans in this song and how he loves them so much.