My young adult son is in an abusive relationship, how can I help keep him safe

I am worried about my young adult son and how to support him. He has past trauma, is neurodivergent, and his current relationship concerns me. The young woman he's involved with is struggling, and despite my attempts to help her during a recent crisis, it feels inadequate. She refuses professional help and wants my son as her sole support, entwining her trauma into conflicts over small issues. My son, not a trauma counselor, is losing sleep, struggling to get to work, and isn't able to take care of his needs. For five days, she's been mean to him, belittling and threatening him while blaming him for things he hasn't done, blaming her trauma on him (even though he wasn't there for it), threatening self-harm, and threatening to tell her friends things about him to get back at him for a percieved harm. I realize this is no longer about her trauma and that my son is in an abusive relationship, yet I don’t know how to help him. She has a grip on him despite his pain, and if she senses my disapproval, she'll drive a wedge between us further. I'm afraid for his safety; the more time he spends with her, the more broken he becomes. I know from my own lived experience that people in these power struggles often need to recognise it themself. I am just really lost and afraid. I am not sure if this will get approved, it might be too personal.