@Reds2004 sorry to read this.
When I split with my exh I also didn't want to hurt him, so kept quiet about the man I started dating.
He was a giant red flag from over 20 years age gap and generally just very stalkerish/love bomb/lying/typical narc type.
Anyway, I didn't go the police because he was my manager and I was scared, but he did similar stuff to what this guy is saying to you. (I don't want to merail but if you'd like to know what he did please let me know) Anyway he never told my exH and left me alone in the end because he was from a nice "well to do" family and mine are for lack of better description, hooligans, so I just said if it carries on my dad will be visiting your dad, kind of thing.
That was enough to deter him and ironically I'd not spoken to my dad for many years, he just had quite a reputation and it wouldn't have been wise to continue harassing his daughter.
The guy went on a did it to another colleague almost a week after I got freedom from his bullshit.
He messaged me about 2 years later on Facebook like we were BFFs and I told him if he contacted me again I'd go the police, never heard anything since.
I wish though I'd gone the police because what he did to my old colleague was actually far worse than what he did to me.
Police. Police. Police.
Also your exH sounds like a good guy, even if its not a marriage anymore, I am happy he's supportive.
And this other dude I can't say enough... police.
Take care and please update this thread, I don't think I speak alone when I say your safety is very cared about.