Forbidden love

For jessica life seems to gone all wrong , she doesn't have money enough to pay the bills, after her parents die in a tragic accident she is independent girl , she had to live alone with her little sister since her 14 years old, she need to work a lot to earn money to her family but she is sick of everything, sick of this life. Sometimes she just wanted to give up and live a better life unite she met a boy named Travis.
Travis was the opposite of her, he had a lot of money , he had a great job and everything he wanted.
The world keeps putting them together but she hated him , he was rude and jerk but she fell in love for his good side.
He changed her life for better than she can even imagine.
They been together for a long time , they had a lot of adventures and sadness but one day she find something terrible that made her move away from him time a time.
He didn't understand what she is doing , why she is going away from him ? He asked himself if he had done anything wrong ? But she the only thing she answered was " we can't be together , our love is forbidden"
Why can't they be together? What does she mean with they love his forbidden