I'd respect his threat of an RO. That's serious. We've seen members on the romantic relationship boards ignore such threats until it turned out to be real, with a lot of legal problems ensuing.
I read your 2016 intro thread. Did he make it through the military academy?
You could certainly reach out through familial proxies as he's demanded. Think, however, that this is a power play on his part where he'll be in control.
If you decide to do this, which sounds legally safe, I'd be brief and short. He's not likely to "listen" or care about your feelings; that verbiage would likely trigger him into reinforcing his view of you in his mind (abandoner, Persecutor).
Can you think of something to write which tosses the ball into his court?
This might help:
BIFF: Brief, Informative, Friendly, Firm This may seem obvious to say, but he doesn't view the world or people like you or I do. He's limited. He may be incapable of understanding the hurt he's causing; or if he is, feeling shame (a core feeling of pwBPD), and doesn't have the emotional tools to deal with it healthily. Instead, he lashes out.