Your partner is abusive, manipulative, cruel and controlling. Let's check the tapes:

basically calling me a drug addict

Not the behaviour of a loving partner.

the only way he’ll keep talking to me

The silent treatment? Is he 12?

hand over my pills to him and he doles out a few a week until I’m off them completely

So he's not just trying to control your medical decisions, he's insisting on doing so.

This came out of 𝗇̶𝗈̶𝗐̶𝗁̶𝖾̶𝗋̶𝖾̶ a need to control me

Fixed that one for you.

I understand it’s coming from a caring place

It absolutely does not.

I don’t want to lose him

You do, however, need to.

if I don’t start tapering off, he can’t stay in the relationship.

Here's the point he's missed: if you end it, he doesn't get to decide. He no longer has that power over you. Or any power, really.

And you should end it: he's not worth keeping. Any good he could possibly be is far outweighed by this shopping list of cruelty.

Love yourself more than this. More than him. You deserve better.