Heyo. Need some advice on what to do about a difficult neighbour.

Location: UK

So. I've lived in my flat (in the UK) for almost 3 years now - it's a duplex attached to another duplex. (Houses turned into flats).

My downstairs neighbour, I'll call him Daniel, has always been aggressive. I struggle with self-harm and every time he's noticed a new wound, he says that "a proper beating" will straighten me out.

He threatens to kill my dog if he barks too much, he threatens to break my windows when I'm not home.

I am also trans, so he makes jokes about that often. (Part of that was my fault, I told him my deadname and explained trans issues to him, I try to help people understand, yeah?)

Recently, because I'm a young man also exploring his sexuality, he's said very lewdly that he listens to what me and partners get up to, and has said "next time I hear you going at it, I'm going to knock on your door. If you answer, I'm joining."

This man is at least 20 years older than me. I am 24.

Legally, what could I do to get him to stop interactions with me?

He scares me. He reminds me of people I don't want to remember. What should I do?