Kelsei's determined to ruin Deannah's life, she will lie to get Deannah's one thing that means the most to her. However it's not lying if you only tilt the truth.
"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.