How come I hate someone I don't know so much?

I've become really good friends with this girl, lately. We're not going out but I would like to. She lives with her grandparents but I didn't know why. Being the moron I am, I asked her why. When she was five years old, her mom died. Her dad was always working and never had time for her. When she was twelve, he let go custody of her and transitioned custody over to her mom's parents without even telling her. He dropped her off and her grandparents one day with all her stuff and no one has seen him since. He sends her a Christmas card every year, but it's always from a different return address label for people who haven't established full residency in a state, yet. How anyone can do this is beyond comprehension and with a girl as sweet as Emily... well, you get my point. She hates him and I don't know why but I hate him, too. I love Emily, a lot. More than she knows. Is it because of how much I truly care for Emily that has led me to hate this man so much.