Hi Mandy.
I don't want to repeat but I felt for you reading your post. Bullying happens. I worked with dysfunctional work groups and I was surprised at some of the childish mean behavior that developed between adults! When I say childish, I am not minimizing the MEAN part, it was truly shocking at times.
After doing this for many years....my personal conclusion is that this behavior evolves at the employee level over time, but the root of the problem stems from the TOP. I have yet to work with "healthy management" that has a culture of employee bullying (excusing a rare isolated incident that is immediately managed).
Leaving and not "fighting" your last job.....you can call it that way. I don't agree. I think your personal health and sanity is far more important. I advocated for one bullying victim once.... to be blunt they came to work for me so I could determine if they should be fired. This person turned out to be competent, professional with a great attitude - despite what she had gone through! I told the company she was just that. They fired her without my consent while I was on a business trip.
So, I share that story out of respect for what she went through, and the fact that she couldn't have persevered in her situation. I do not know your specifics of course but please don't beat yourself up over that decision. It was likely the best one.
There are great workplaces out there, I promise, I have seen them. As for your letter. Please don't. You are searching for understanding and acknowledgement (which any of us would) but you will not get that from the employer you left. Leave it with the dentist story, that is fine.
There will be another job. Maybe you aren't ready yet, maybe something there struck you wrong on some level. Doesn't matter. You will have another opportunity and if you are better healed from all of this, you are likely to make a better decision and find a great place where you can be happy and successful!!
Worrying you did things "wrong" or are making the wrong choices is normal. I have heard your words from others in your situation. It is confusing, you may have been misled and lied to if the company is concerned about litigation. Trust advice from friends, people that have no vested interest in your outcome.
Do not put anything in writing to any employer, past or present. Once it is "out there" you cannot take it back.
Vent here, vent safely but take care of yourself first and foremost!!!
I'm truly sorry you have experienced this. Whirlwind