It is a sad story, and I am sorry that it happened... but it did. You knew your own mind and you wasn't ready and that is really a good thing. But the going back and forwards was a real un healthy thing to do for the both of you, and I feel that you gave him each time a little false hope!!! you miss read the letter because at that time you didn't want to see it. You had and experienced relationships and now your at a loss you want him back. Its not fair really, to the both of you. You need to move on, he'll always have a piece of your heart weather he realises it or not.
If you ever had a relationship a proper one I feel that he will make you un happy, to hurt you. Or it just wouldn't be a healthy relationship, it would be a relationship for all the wrong reasons.
I have experienced, you can never go back to an ex.... 9 times out of ten it will never work out as you would like.
Learn from this experience, grow from this experience, your a beautiful strong person and you will find some-one who would like to love and grow into a relationship just as much as you. Then you know you did the right thing.
Don't go and beat your self up any more, you don't need to feel sad or guilty.
Hope things work out for you