I don't know how you know HER mental status but the word of a scorned woman has little credibility to strangers. It's not your job to warn her b/c it's obvious to most people he's not a normal guy.
As for the FB stuff
I would not respond to him or his posts or bother telling friends "HE is the one who is nuts". If he is ranting how you say, and also posting that he's "in love" with someone decades younger, it speaks for itself. It says it all.
There is nothing YOU can say that would do more than simply remaining silent, as he loudly self destructs.
I also worry about your tone, and the way you post "sounds" so fast paced that i worry you are spinning your wheels a lot and spiralling. Do what you need to do to PROTECT yourself but don't punish him. That's not your job and it takes so much damn energy to be angry all the time.
Detach BIG TIME from this man as he careens around banging into lives and involving strangers in his drama.
Don't accuse him of needing help. It does NOT help him get it, and it usually triggers a heavy duty reaction in them. But just, Take a breath, and get to a safe place.
M: 57 H: 60 M: 35 yrs S30,D28,D19 H off to Alaska 2006 Recon 7/07- 8/08 *2016* X = "ALASKA 2.0" GROUND HOG DAY I File D 10/16 OW DIV 2/26/2018 X marries OW 5/2016
