Octavia looks upwards, looks at the sky and thanks the stars for not taking from her the two most important persons in her life.
She thanks them because she doesn’t know who
But she remembers her brother telling her about the greek gods and those who have their home among the stars, those who become them. She remembers listening to his voice as he speaks of Andromeda and her mother, Cassiopeia. She remembers being in his arms at night as they wait for sleep to come
She remembers how the gods thanked others by taking them to the stars. She had never really understood why people was so captivated by the stars, but that day, when Bellamy fulfills her dream
So she decides she’d thank them, because she has no one else to thank.