Sienna and Saige could not be separated, until one night when Saige pulled a huge prank on Sienna, embarrassing her in front of National News. From then on, things between them changed, forever.
"YOU ARE THE BIGGEST MISTAKE OF MY LIFE"
That's all she needed to snap out of her illusion and hate him forever.
Leaving was all that was left but again his family hurt them and now the only way to stop th is to destroy them.