If you’ve been with your partner for 6 years, you should know her pretty well. Has her behavior changed? Approach her honestly. The man had a motive for saying what he said, benevolent or otherwise, but honestly it’s irrelevant here. This is about you and your partner. Where do you stand—are you interested in moving on from the relationship or working through a big issue like (possible) infidelity together? There are no right or wrong answers, just what is right for you, how much value the partnership adds to your life, and how you can best move forward in a healthy way if infidelity did occur, whether that’s with or without her in your life. Relationships are built on trust and communication. Start with an honest appraisal of yourself, then discuss what you were told with her. If you have to start snooping or trust is otherwise lost, walls can be built that will be difficult to overcome in the future, whether your relationship ends or not.