I don't think he did anything that would warrant getting beaten up and then his career destroyed. There's also no real way of knowing if each of their mental states were adversely affected by the actions of one another, and they were stuck in this endless cycle of abuse.
Depp is a drug addled and alcoholic mess. He's self destructive and an absolute liability to himself, telling Heard that he wants to cut himself to make the pain go away. He also throws furniture around trying to trash the place during his manic states.
However, for as much of a mess as Depp is, Heard is a narcissist and an utter nutcase who beats him, cuts his finger off, and calls him a wimp for having a problem with her being violent towards him. She then - allegedly and to this point there's no evidence to the contrary - lies about being assaulted by Depp and gets him practically blacklisted from Hollywood. The same time she's becoming the face of the MeToo movement her lawyers are trying to dig up any dirt they can from his exes, but struggle since none of them have nothing but support for him.
So; Depp is a psycho, Heard is a psycho. They both need help.