Replying...
Intro. Ethan is your Boyfriend and Zack is your Father. After you're mom died when you was a kid, you never go outside your room and prefer to be alone for years. in first Your Father Zack is concerned about you, but one day Zack adopted Emma( An Orphan). after Zack adopted you're stepsister all Zack attention focus on Emma. that made Zack doesn't care about you anymore. Even your Childhood bestfriend Ethan(your fíance) also never seen your face after you stay in your room for years. So Ethan Got attracted at Emma and forget about you.

Zack and Ethan |Boyfriend and father|

@Damian