I'm so sorry to hear that this happened, of course. 
So, let's take the letter line by line.
Over the past couple of months I have been doing a lot of
self-evaluation. I am seeing that there are a few aspects of my life
that I am unsatisfied with. One of these aspects includes my
relationship with you.
Do they need to know this? It's obvious you've been doing some self-evaluation, yes. Am not sure what this adds to the letter, though.
I am requesting time apart from you and the family, including loan
payments, to sort out why I have conflicted feelings about our
relationship.
Your parents have been extremely abusive all your life. And... you are unsure why you're conflicted? Obviously, you're not. Why then tell them that you are? It certainly eases the burden on them. Can I ask about the loan payments? You're tied to your parents in some financial dealings, I take it?
It is essential for my growth and well-being that I allow myself to analyze our history and current relationship objectively.
It absolutely is. But again, why justify your actions to them?
I can't provide you with any sort of timeline of when you might hear
from me. I am basically writing you so that you won't worry when you
don't hear from me. Please respect my request that you do not contact me.
But they will "worry." They know what this letter is. Nothing you say - assuming that your parents are abusers who completely deny the past - is going to prevent them from "worrying" their victim is getting away. I hate to say this, my friend... but I can think of no one who has deFOOed and not received contact from their parents. If your parents are abusers and if they deny the past, and if they set you up to rationalize and explain away their every crime... why are they going to take your preferences into account now?
I'm sorry for being so terribly annoying, and asking so many questions. But if you don't owe them anything... don't give them anything.
again, Marisa.
We have reached the open sea, with some charts, and the firmament.
http://montaignesheiress.wordpress.com/