No, you dont have to write a termination letter. You let him bully you into doing it .. if you felt like you were going to be injured physically if you did not then you need to file a police report ASAP for assault.
Now, you dont state what state you are in but in most states, if you quit, you get zero for unemployment. (thats why they ask for termination letters..ie you quit, we did not fire you)
On the positive side, if you did quit it would look better to your next potential employers as opposed to being fired (unless your firing had nothing to do with your performance-loss of business, out of business, etc.).
You can threaten to quit & say that these work conditions are too bad to work under but these are not statements of quitting - just complaints & threats of quitting.
If he said your fired, write a letter of termination, then its up to the unemployment commission to determine if you were fired or quit (a police report would help in this assessment).
If you think it was because you are an immigrant, then you can file an EEOC complaint. From the facts stated, it doesnt look like it but you are not a mind reader so you dont know why you were really fired. A civil suit is an option .. you may file an EEOC complaint & wait for a result of their investigation before filing a civil complaint. Some attorneys will talk to you for nothing too, so you should seek one out to talk to (I am not an attny).
I have been asked to write termination letters & I refuse every time .. they yell etc but I just walk out the door.
Forget people who say you need to talk to your boss all the time about working conditions - you can speak to HR too .. its only a job not a life & death situation.
Get a new job with nicer people and enjoy life. Forget about these dopes. I have worked for people who seemed nice & ended up being complete jerks - I walked out of several jobs because of that; life is too short to deal with jerks 8 hrs of every day.

