If I were you, and if you were really serious about this matter, and even though it might cost you some money, you ought to consider talking to a lawyer. You might even be able to call a lawyer and they'll help you for free if it only takes a few minutes.
I say this because I am NOT a lawyer and giving you advice on this matter could work against me. Now, I bring up this idea of a lawyer because if he [does] beat her, even killing her out of a fit of rage, if anyone were to find out that you were aware of his abuse, you could be held liable.
What a drag, Snacks!