MY SISTER WAS KILLED IN 9/11?

me and my sister (workers) and my father ( firman) , were in 9/11. me and my dad made it out alive,but my sister unfortunately didn't. my dad always tries to compare me to her, always speak abouts her, and he says something and i don't understand it and he'll say something like, you sister would understand. i know he misses and so do i , but i can't have him doing this.at his firehouse there is firemen who really likes me, but for personal reasons i don't know if to get with him. and i overheard my dad saying to him, you would have liked her sister, very intelligent and so on . how can he say that? hes been doing it for 8 years, and my sister and i were very close and went through agony of not only being in 9/11 but losing her, and he added to the torment. last week he said something again when i visited the firehouse, and i lost it and shouted " well ddad im not lydia, ok im your other daughter, shes dead , ok , start remembering that and stormed out in tears. i feel so bad what should i do?