You’ve done Drs, CAMHS, no ND or ADHD
Next time I wouldn’t be calling a Dr but the police, he’s a harm to himself. Although I don’t believe that. You’ve already said he manipulative. He can obviously switch it on and off. I wouldn’t even threaten it, I would just do it. If he’s at real harm to himself they can call the right people, but I’m guessing he will shit himself and suddenly snap out of it.
By not contacting the girlfriends parents you are seriously putting her at risk, it dosnt matter how besotted he is now he has a violent streak especially when he can’t get his own way, you have a duty of care whether you like it or not. Right now you sound like all those mothers of violent men who make excuses for them.
Maybe you publicly pulling him up on his behaviour is what he needs to know he can’t get away with this.
Id also record him, show the Drs, school police and girlfriend if she dosnt believe he could act this way. Otherwise you’re allowing him to get away with it.
My friends has called the police on her 12yo ND, Autistic, ADHD and other issues son because of his violent temper. He’s bigger than her now so she needed to do something. One of her big fears is girls, if he can attack her he can attack a girl who can’t defend herself. The community police were happy to talk to him, tell him his behaviour isn’t acceptable and basically tell him what’s going to happen to him if he keeps it up. My friends DS has Sen issues which file his behaviour, from the sounds of it your DS dosnt, he needs a massive wake up call.