As I thoroughly investigate all compelling leads, I have seen the Instagrams at various points of both Luke's sister and the boyfriend; and can confirm that the story he tells is accurate.
The bigger mystery is how her boyfriend earned so much money to literally live among celebrities in Beverly Hills, and how, despite being twice her age, met a girl who was at the time 16 or 17, literally on the other side of the world, and courted her over years into moving in with him in Los Angeles. But the tale Luke tells is truthful.