Best Friend's Boyfriend

[notsurewhattodoaboutthis]

if your best friend's boyfriend (of a few months) swore at you and threatened you that if you text her again he'd call the police and blamed all of your friends problems on you (actually said "it's all your fault"), and told you that you were mad and need help (I have PND, but just started taking sertraline and have a baby), would you be scared of this man? And would you be upset if she got back with him after this?
Even after she explained that it's not your fault, he was out of line...etc.

His behaviour is clearly not normal. If he was like this with you, presumably as well he treats her just the same of not worse. This man has serious problems which she cannot fix. She should not try to either rescue or save him. If he is like this after three months then what is he going to be like after a year?.

Why is this woman with such an abusive man?. She needs to think carefully.

I wouldn't be scared of him, I would be telling him to call the police because I was going to give him a fucking hiding.
I would be slightly concerned if my friend went anywhere near an unhinged weirdo like this though.

Her ex tells her that he's just "trying to protect her". he's never been this way to her. Only this once to me.
She has a lot of stuff she's dealing with right now and does some things that worry me (and him). I feel so because she's not sure if she will get back with him or not but she's giving him a chance and I think she thinks it's all my fault, too now. Even though she's been through pnd herself. I'm at work but fighting tears. Feel like I'm losing my best friend. My husband is being unsupportive of things at the moment and I just don't know what to do.

so, what happened exactly?

Sounds to me like he is trying to isolate her from any potential support. Abusive men often do this. Make sure their victim has nobody in life. Then they can do whatever and know they have nobody to turn to. Also start with the "I'm the only one who cares about you..." mindfuck.

I'd get in there first by showing the police his threatening text.

What are you supposed to have done to her then?