Fiance's Past - Open and Honest?

I've been dating my fiance for over 2 years now and soon to marry. She's always stressed the importance of being open and honest with each other which I agree is important. When we had the "past relationships" conversation, she was very vague and reluctant to share any information. I know that she dated other guys etc. and I would be a fool to think otherwise... I guess im more concerned about the fact that she's not being open and honest like she's promoted us to be . I know that she had a thing with a guy that is close to her and her family, but she doesnt / wont talk about it. I'm more concern at the fact that she's very stand off about the subject and feel she's hidding something to prevent an argument or making me angry. What happened in the past is the past and it would have no impact on our relationship unless something accured while we dated, however, I'm more upset at the fact that she is not being "open and honest" which is causing me to have doubts. We love each other very much and i'm trying to forget our conversations or lack there of. Her not being honest is negatively impacting my trusting her and it's driving me crazy. What do I do?