I have something uncomfortable to ask about someone (who may have borderline personality disorder)

[enough]

2. I don't think there's anything you can say that will help. Trying to explain what you are doing,

or what he should do, will be no use. You can't help him. The only thing to do is to completely cease communication. Blocking phone and e-mail communication is probably best.

I'm saying this with the assumption that you don't have kids or other relatives you are both responsible for, so that a call from him might be about an emergency that you have to deal with (not an emergency about him only).

There is nothing you can say. Talking or communicating with him is just continuing the relationship, even if you are talking to him to tell him you want to end it permanently. You have to stop communicating.

I don't know what to do about your fear of him. Please trust your sense that he may be dangerous. But talking to him in order to keep him from getting angry is never going to end or change the situation.

I hope other DUers will have better practical advice.

Wishing you well in this difficult situation.