How am I supposed to feel about my nephews condition?

I have a nephew who was born with the shortening of the external limb and a truck load of heart defects. He's three years old now and I'm going on my 13th birthday. I've grown used to him having this condition and I'm madly in love with him. I'm worried because I'm having these urges that scare me. I'm constantly feeling that I want to know what it's like to choke someone to death and I get furious and I just wanna hurt people. I don't want to hurt them severely, just enough to satisfy the urge. I've always been a calm person never angry at someone for no reason. Am I angry at his condition? Or am I just angry at myself for not being able to help him? Because sometimes I feel I'm a bad person for being angry at his condition.