What are you trying to accomplish? To me, it doesn’t sound like you have moved on from the events of the past. This sounds like you want her to feel your pain. I can appreciate you feeling you need to be honest, but sometimes you have to go back to these 3 questions. Is it true? Is it kind? Is it necessary?

If writing these words help you move on, great. Write them out and burn them. But I feel that giving your fiance this letter will revisit and prolong the pain you seem to still be feeling. I wouldn’t personally read past the first paragraph. Who wants to have their past mistakes thrown in their face?

I worry I’m being a bit harsh here but ask yourself what this will give you?