Boss Threatening To Sue Me If I Don't Keep Working - For Free

Seeking high-level employment law advice before retaining my own attorney (which I will likely do).

I'm currently in a very odd "employment" situation. The company ran out of money last year and I haven't been paid at all in 2024. I tried to resign (for various reasons including finances) and was told that my resignation wasn't accepted. I was very shaken by the threats to "ruin" me if I didn't keep working (for no pay) so just...kept doing the work that was assigned to me. (I would really, really appreciate if everyone could be kind and not call me stupid for doing this. I know this isn't right, but he boss is someone I have known for many years and who has, in fact, "ruined" people professionally, just out of spite.)

It isn't possible for me to keep working full-time (or at all) for no money. I informed the boss of this and he threatened to sue me for "breach of fiduciary duty" if I don't keep working (for free, indefinitely), saying customer relationships will be irreparably damaged. (He threatened, specifically, to find past instances of mistakes I made, during the time that I had been paid, to demonstrate how I had damaged the company.)

I know I likely just need to inform him I'm not doing any more work, lawyer up, and not communicate with him directly anymore. But I'm wondering if, based on what I have said here, he would in fact have any potential cause to sue me for "breach of fiduciary duty"? Are such lawsuits - employer against employee - relatively common and/or ever successful? Is there any obligation that I would have, as an "employee," even if I haven't been paid in a long time?

I'm in the US in a major metropolitan area (reluctant to give more specific location details). I am a regular W-2 employee (or at least I was - I don't know how I'm classified when doing "volunteer" work for months). My position does not involve managing money (I know "fiduciary duty" is not just that, but wanted to clarify I don't have access to any company bank accounts or anything like that.) The job does involve serving clients/customers but it's not health care or anything with a lifesaving component.

(Yes, this is a throwaway account.)

Thanks for your help. (And again, I know I'm likely a fool, but please don't rub it in - I just want to fix the situation going forward and avoid getting sued on top of all the money I've already lost here.)