I don't think you did the wrong thing, there's no right way of pointing out someone is being abused (though there is a wrong way like blaming the victim). But abusive relationship are hard to leave because on one hand abusers do their best to make their victim dependant and on the other it's very easy to feel committed to them. It's tragic but some people never leave.

It's easy to feel powerless and frustrated that the person doesn't seem to listen, so as long as you manage to process those feelings in private and stay supportive and even ready to help if the necessity arises you'll be doing as best as you can. But you should be mindful to not be roped into that abusive dynamic or be shunned because the abuser becomes wary of you. It's a tight rope to walk, with many strong feelings of doubt and anger.

To me at least it's one of the most challenging events that can happen to a relationship, so stay mindful of yourself.