AIBU to think it's totally insane to stay with someone whose even threatened to harm your family member?

[Supernova12345]

I won't go into all the details, as could be outing. Basically, my Cousin's partner had a brief affair with his ex girlfriend, my Cousin found out, was understandably upset and sent him packing.
A few weeks later cousin's now ex turned up at her home, cousin was upstairs, and her adult DD (who was visiting) allowed him in and told him exactly what she thought of him.

My cousin said she could hear her DD shouting at her ex, but then, as she came downstairs, the situation had turned really sinister as her ex had a knife in his hand and was threatening her DD and also DD's husband (who'd stood in between them both to protect his wife)

Thankfully, DD's DH managed to get the knife off him, and got cousin's ex out of the house. For some reason they didn't call the Police over this.
Now, it turns out that my cousin has decided to get back with her partner, and says that he only grabbed the kitchen knife to scare her DD and her DH, because her DD was going berserk at him, and he would 'never have used it'.

AIBU to think how the F could someone not only get back with someone whose threatened physical harm, but especially to their Child?

If I was her daughter I would never speak to her again.

I hope she changes her mind and reports him too.

Some women do value the attentions and affections of men above their children. My mother was that way, and stayed with men who did deplorable things to me.

Can you report him? Brandishing knives at people at close quarters is not a thing to be messed with.
And yes of course she is doing the wrong thing and her DD would be right to avoid any contact.
He's a dangerous man and anyone under any illusions about him must have been living under a rock for the last week, the news is full of them.

Does your cousin have a history of choosing toxic men OP?

I'd say there's a history that you might not be aware of. Your cousin is obviously dysfunctional and in a highly dysfunctional relationship. I would support her daughter to keep her distance from the pair of them.

That's the thing, her DD said originally that she wouldn't speak to her again if she took him back, but now, it's as if her mum has convinced her that her partner wouldn't have acted on anything. It's as if everything is being minimised.

Sorry to hear that, it's disgusting what people will put up with, no matter the affect on their own children.

I've contemplated reporting him, but I'm unsure if my cousin would back me up. It seems as if he's convinced her he's no real threat, and in turn, her DD has been influenced by them I think.

There's been one or two very questionable relationships she's had in the past, yes.

I do feel as if I have to tread carefully, and I've stated my opinion, but I fear that my concerns aren't being taken seriously.

I would be very concerned; Thurs situation has tragedy written all over it.

Look at the impact on the DD; she’s already been manipulated by her mother to accept very frightening levels of violence.

I would guess there are other things about this abusive and dangerous man that aren’t openly known. I’d be trying to support both women and remind them that this man is an abuser. It cannot be one incident

Honestly he threatened her DD with a knife, it could get much worse. I’d be really worried this could escalate at some point and someone could get seriously hurt.

But yeah if anyone threatened my DD with a knife I’d be calling the police.

I agree, it can't be one incident, but my cousin insists he wouldn't ever hurt anyone. I don't know Wtf she thinks he might have done if her DD's husband didn't intervene!

Regardless, the very fact he even picked up the knife tells me he's dangerous.

I agree with you too, and it doesn't matter if her DD was ranting and raving at him, he shouldn't have even contemplated picking up a weapon.

What's the DD's husband saying now? You say if you report the cousin might not back you up but would he back you up? Or would he report?
Do you know the DD's husband well enough to ask him how he's feeling about the whole thing?

Did he go with the knife? He sounds very dangerous. It's really hard for you as it sounds like they'd aren't going to listen to you.
I'd be tempted to report it to police anyway so it could go on file for when there are more incidents (which there will be, sadly).

I don't know him well enough to know what he's thinking of the whole incident really, maybe he's thinking it was a 'one off' too, especially as he and his wife are quite young. They maybe don't realise that history has a way of repeating itself.

No he didn't go with the knife. All I can gather is, he went to see my cousin to talk things through (and beg for forgiveness over his cheating), but her DD started on him, and he then apparently picked it up, I'm unsure if her DD had pushed at him in temper.

However, if she did, it still doesn't excuse him picking a knife up. It's a good idea to have it down on file, although I'm not sure if the Police will question him anyway and then it could inflame things again.

He is thin skinned, immature, impulsive and controlling. I would report it to the police: anyone who enters a house and picks up a knife to emphasize that they need to be listened to is someone who is prepared to threaten people into complying with their wishes.

It could be a tragedy; better this vile man has his wing’s clipped than dead women when his temper gets the better of him.

Please report it @Supernova12345
As you say then it's on file in case there are future incidents. You can't refrain from reporting it for fear of aggravating him further, that's giving in to his violence. I mean, you can, obviously- but personally I think that's not the best decision.
You sound like the only grown up in the room. It's a hard place to be, having to take responsibility for making a decision that no-one else seems to be willing to make.

Thanks for your comments, I'll be concerned whether I report him or not, although I more than likely will. Although, even if it's on file, that won't stop him and his temper the next time he decides to pick up a knife or something else.