When you're being abused, chances are you know you are. But you feel guilty for being in that relationship so you gonna rationalize it. Even defend it. The more your relationship os criticised the more you double down on it. That is why abusive relationships are so hard to leave.

So tell your friend over and over again, you do not judge them for being with a shitty person. Assure them there will be no "I told you so" if they ever decide to get out.

Tell them you're willing to do whatever they need, should they need to get out.

And do all of that proactively!

Said friend told me they suspected what was happening but I kept relativising it. Which annoyed them and drove them away.

And they were stunned when I told them "yes because I wasn't safe with you. Because none of you gave me any reassurance that you'd be safe. That you'd not be judgemental."

Among all my friends, in the end there was one person that finally said what I needed to hear. One.
Don't be like my friends.

This isn't just my friends. Both in my own life and as a social worker I see this helplessness of people who know someone in an abusive relationship so often.

Said friend asked others what to do and found no useful advise.

Every time I have a client who just escaped an abusive partner, their friends knew and did nothing useful. And it often made them loose all trust in their friends.

That is why at work, when I see a client with their partner and suspect abuse, the last thing is to ask them if they're being abused. That is a useless question.

I take them aside and tell them unprompted that abuse victims blaming themselves for staying with their partner is a very common reaction and that here, we will not ever ever judge that just one bit. And that we offer any help needed. Even if it involves plotting an escape plan.