Why does Avery despise Drake, Libby's boyfriend, in the novel, The Inheritance Games?

Avery despises Blake because he is emotionally abusive to Libby, and he treats Avery terribly. Avery also fears that it might just be a matter of time until he physically abuses Libby.

Avery very much dislikes Blake because he is abusive towards Avery's sister, Libby. He also treats Avery very badly. He gets worse throughout the book and Avery tells her sister, Libby, that she should break up with him for many reasons.