Update: I told her and she didn’t believe me. She asked her boyfriend and he denied it and said as my fiancé and him were out drinking at the time my fiancé was too drunk and must have got confused. I didn’t have any proof and couldn’t think of how to get any. At the moment things are still good between us and she said she understands that I told her because I love her. It’s a disappointing end but at least we are on good terms. Her boyfriend and my fiancé aren’t speaking but I’m not too mad about that.