Friend went back to abusive relationship

[Dooooooooo]

She's been with him around 5 years and it's been on and off a lot of the time, so when she tells me for the umpteenth time they're back together I politely tell her I'm happy for her but inwardly roll my eyes.
Last week she confessed to me that he slapped her in the face and shoved her during an argument.
I was very shocked but it shows you can never truly know. My advice was to leave asap. I have previously been in an abusive relationship, funnily with similar circumstances, slapped and shoved, the ex also threatened to smash my head in. Unfortunately I didn't leave immediately, I was very young and had no self esteem. Thankfully that relationship ended 8 years ago.
Anyway, she went to stay with her Mum and seemed adamant it was over for good.
I've had a message this evening saying they've sorted it out and are back together. I honestly don't know what to say...
If he's done it once, what's to stop him doing it again? Especially now he knows he can get away with it.
I don't want to say the wrong thing and upset her. I don't know what to say, domestic abuse is never acceptable, I suppose all I can do at present is be there for her. It's sad though but not uncommon. How could I support?

That is a terrible situation for her, and a difficult one for you!

I agree with you, keep on being there for her. Let her know by your actions and words that you support her.

I would reply and say that as her friend you will always be there for her and support her however also as her friend you cant pretend to be happy for her because her relationship is really abusive but you are there for her if she wants to talk...

When I was experiencing DV these were the most helpful friends. The ones who abandoned me were not helpful nor were the ones who pretended like everything was great.

Don’t say anything to alienate her - eg, you have to leave etc.
Say you’re always there for her. It’s a really tricky line to walk

I have a friend who has returned repeatedly to a coercively controlling relationship.
She knows what I think but also knows I am her friend and will support her and be there for her
But it's hard sometimes to step back.

It's always difficult, he has her completely caught up in doubting herself and has convinced her of his version of events. Only she can see the cracks for herself, but she can't do that until she sees the value in trusting herself

Thank you. It's so difficult isn't it ..
A few years ago I had a male friend with a girlfriend who consistently accused him of cheating. She also sent me an angry message once for daring to talk to him, she clearly had a lot of issues which was a shame.
He told me once that she'd lied about pregnancy to him and deliberately stopped taking contraception, something like that.
He constantly complained about this relationship so one day I said to him, why not leave? I also told him the pregnancy lies were not acceptable.
Anyway, a week later he turned on me. He told me he'd spoken with her and decided that what I had been saying about her was out of order, and that we weren't to have any further contact.
All I had done was advise him to leave a toxic situation. Unfortunately he's still in that relationship and I hope it's worked out for him. However I lost the friendship, I feel that I have to be very careful what I say now as some people simply don't want advice.