I think the OP understands she blew it by leaving the document on his computer. Yes, he read it but then my guess is most people would do the same. The question now is how to move forward. Given what was written had nothing to do with the fiancé it shouldn't be his business.
On the other hand if he's worried the OP will treat him the same down the road perhaps they should seek a professional counselor before setting any marriage date.