I don't know the time gap when you got yourself HIV tested after unprotected sex 2 years ago. If the HIV test was ELISA test and was done anytime before 3 months (after the exposure), such false negative reports can be a possibility.
Now, whatever has happened is beyond any repair. In my opinion, you must not hide your HIV positive status from your would be wife. Please talk to a HIV counsellor and devise a strategy to let your friend know about every thing. She must take a considered decision on this issue. You should also be prepared to accept whatever she decides.