I hate the resident asshole in our apartment complex
What is your reason for hating this person?
I have been dating his sister for quite some time, then he suddenly slept with her. Now they are in love. He also threatened to kill my dog if I told anyone about what I discovered.
It's understandable that you disagree with and dislike this person. If threats are being made towards you, you should alert the police as soon as you can.
I'm going to tell everyone in the world about him.
Threats to your dog are not to be taken lightly. You need to protect yourself and your dog by telling the authorities.