[35M] I've uncovered details about my wife's [37F] past that are difficult for me to process. I need some support.

I'm posting anonymously for obvious reasons. So, yesterday, my curiosity got the better of me. I came across my wife's old phone in a drawer, guessed her PIN, and decided to take a look. I know it's wrong, but I was curious. I didn’t find much in her photo library, just a few softcore selfies. That wasn’t too surprising, as I figured she tends to keep things clean. I couldn't see her chat history because she usually deletes those conversations anyway. However, I did come across a period tracker app. As I swiped through it, a realization hit me. The app allows you to track sexual activity, including whether it was protected, and even notes about orgasms and contraceptive use. It turns out she hasn’t been on birth control for quite some time, despite tracking a few months when she was. More alarmingly, she had noted down various names—some appeared consistently for weeks, while others were one-offs. Several of these encounters were marked as unprotected, and I saw entries for two threesomes, one of which was also unprotected. Unfortunately, I can only see a little over a year’s worth of data because she changed phones, so I don’t know if this behavior has been ongoing for longer. She's told me before that she had been with three guys, never had a one-night stand, and definitely never had a threesome. All of that appears to be untrue. I had my doubts before based on certain hints she dropped, but she would get upset if I ever brought it up. We've been together for three years and have a one-year-old daughter. I’m really at a loss about how to address this without revealing what I found; I fear that could end our relationship, and I don’t want that. Right now, I can’t even look her in the eye or express my feelings. How should I approach this situation and figure out the next steps? TL;DR: I discovered that my wife has significantly downplayed her sexual history.