Can my employer sue me as retaliation for quitting even in an at-will state?

I have multiple issues that I need legal help and advice on. I was the web developer for a company from September of 2008 to April of 2009. I was their only IT professional on site and had to wear "multiple hats" to do my job at a very reduced pay rate (no benefits) with hours worked both on-site and from home totaling over 80-90 hours per week to conduct my job productively. Under no circumstances, even with trying to work something out, did the owner of the company have any interest in providing reasonable concession to me so that I could reduce the hours worked in order for me to be able to continue to work there. When it became clear that I could do nothing further with the company, I made the decision to resign. Now, note: while I was there, there were health code violations that did effect my health but I have had no resources or insurance to actually go more than see a doctor for the very expensive tests involved (more than $1000) to show that my workplace was effecting my health. Secondly, the owner of this company consistently made lewd jokes about things that I made clear I didn't like to be around, and worse also started to obsess over my own wife making comments about her to me directly (even in front of his own emotionally battered wife) and even eventually giving my wife improper gifts with said comments. That amongst sever incompetence at managing a business caused me to fear my future, career, health, and well being, by staying there and I decided to leave.That should have been the end of it.

Instead, I am now being retaliated against for quitting my at-will job, reporting their office to OSHA, and also now being retaliated against further for filing unemployment benefits claims that were approved when they found I was working in a hostile work environment based on the evidence I provided the state department.

This individual continues, even to this day, to threaten me with legal action and has claimed to have contacted the "FBI IT criminal division and DA office" for supposed sabotage and extortion, of which I have nothing to do with. This individual is bullying me into doing additional work for him for free. That is the only goal here outside of his personal enjoyment at my distress.

This individual also has violated federal labor laws and also has not paid my final paycheck in full as additional retaliation for resigning my position. I signed no contracts with this person, nor am I under any obligations to his company for any work left undone.

I need to seek advice on what the heck I can do here to stop all of this. I have a right to live my life and get on with my life. That is what I intended to do when I left that job. Yet he somehow things he owns me.

I have been having trouble sleeping because of all of this and I am about to collapse and end up in the hospital anyway because of all the undue stress from this. I need help with this somehow right away as I need to separate myself from this and not feel threatened or bullied by this man any further.

I start a new job very soon. but now I fear that once he finds out where I work (he runs my credit without my permission periodically) he will harass me there and call my employers with further lies if he hasn't already done so to other prospective employers in my job hunt thus far (I mysteriously had a job offer declined days after it was offered to me and I, at the final interview, was told they will be contacting all references and past employers).

Do you know of any actual criminal complaints I could file with law enforcement? It is very bad how little an employee is protected here in the states. This guy has claimed to me on multiple occasions that he is above the law and he would easily ruin me if I quit. So far what I have seen, that can be the case.

Additional information, his most recent harassing and bullying e-mail makes claims that he is going to sue me for "your all salary we paid you plus our business loss of $500,000 Plus etc." (he doesn't speak English very well)

And in this e-mail the employer cc'd a copy of this to what he claims is his lawyer (lawyer in which I tried calling today to confirm that he is representing this employer, but he was out of the office).

Thanks

I forgot to add that he is making claims that he is losing business (but that is solely because he is unwilling, to hire a replacement at the regular salary which is more than twice what I originally agreed to work for on average)