You're right. I'm just overthinking and panicking.
I'm not sure what the police will do
Very belated but I (unfortunately) have some experience of this
You don't need to decide if it's an overreaction or to know what the police can do. That's their job, not yours. That's why you report it - so they can give you advice, decide if there is anything to investigate further or any action to be taken. And so something is recorded somewhere, so a paper trail is started. If you want support you could speak to an ISVA but in my experience they're not hugely helpful. But they do exist.
Same for employment lawyers - you don't need to know all the ways your employers have
ducked up, that's ACAS/your union/any other employment lawyers job. Find someone reputable, explain what is going on, and let them support you & tell you what they're going to do/how they can help.
There is a lot that can be done by the police before reaching the "taking this to CPS to decide if its in the public interest to pursue as a criminal matter with a sufficient burden of evidence" threshold. Someone being charged/convicted isn’t the only possible route.
If something doesn't merit a restraining order, the police can serve a harassment notice. If they think its of enough concern it can be recorded in a way they can share it in future under Clare's Law. If he currently or in the future wants to work anywhere he needs an enhanced DBS, it may impact that. There may be other similar reports, and your report could lend weight to them or another police service deciding to take action/investigate further. It may make other victims more credible. It may show him he doesn't have power over you.
It makes me really sad to see how you are being victimised, not only by him but by your employer and colleagues. I hope you're signed off work sick at the moment, and I hope you have some tangible support. None of it is your fault, and you've been let down and victimised by many people - but you do have some power, in that you can reach out for help from people who may be able to hold him and/or your employers to account.