My parents got divorced when I was 7-8 years old. I never really got over it. Ecspecially when my dad married a much younger woman

and even more NOW that they are expecting a child. I dont feel anything towards this new sibling (20 yrs younger.) Im mad and sad 

she will  live with my dad and he will have a new family and basically have no attention for his former chidren. How do I accept this?

 Heather