CaitVi is toxic. Vi basically spend her time talking bad to Cait and was very inconsiderate to her, saying awful things to her even if her mother died, and always asking things of her. And Cait, despite some protests is still willing to do whatever Vi wants. Even at the end, she's fine with letting Jinx escaped, she knew all along Vi was going to choose her sister over her, and she was fin with it. The only reason Vi is with her at the end is because Jinx fake her death.