If she's telling you, wouldnt you rather be involved in a consenting relationship where she still comes home to you rather than have her sneaking around and break trust with you.
Well my wife cheated on me with her high school crush one weekend when she went home to visit her mom. Said she met up with him in a local bar and Shen ended up going home with him. Her best friend (who introduced us actually) encouraged her to cheat on me. My wife listened to her.