Kylie
About
Kylie is not actually Ian's older sister, but his biological mother; Ian was conceived as a result of Kylie being raped by her biological father when she was 14 years old, and then passed off as the son of Kylie's mother — who accuses Kylie of only having Ian in order to spite her.
Kylie ends up in prison again after attempting to kill her boyfriend, who turns out to be the pimp whom Ian had been sold to by Kylie's mother. The ex is implied to be suffering from an incurable, transmissible disease that he passed on to Kylie, which caused her death. When investigating, Ian is told that Kylie passed away as a result of pneumonia.