My Cheating Husband's Secret Admirer

I'm Sarah, and I've been married to John for five years now. We were always happy together, but lately he seems distant. Last week, I noticed something unusual in his email inbox: a folder labeled 'For Her Eyes Only.' Curiosity got the better of me, and I opened it, discovering messages from someone who called herself 'His Secret Admirer.' She would write him sweet nothings every day, telling him how attractive she found him. It was all very flattering and innocent-sounding at first. Then things took a turn. The emails started to describe her fantasies about John, making it clear that this admirer wasn't just playing the friend zone game but had real intentions behind those words. She described scenes in vivid detail, ones I never would have thought him interested in, and ones we'd never explored together. The most recent message was chilling: she said she'd been watching us from afar, finding every moment of intimacy between John and me thrilling to watch as if it were a private show just for her. She wanted more than just words now; she wanted real encounters too. And I couldn't help but feel...jealous? How do you handle something like this when your marriage feels like the last thing on his mind, yet another woman seems to know exactly what he likes in bed? Am I the asshole for reading these messages or should I confront John and talk about our relationship before it goes further with someone else? What would you do?