USB Debugging to Get Info on a Liar

So I found some info out and I was basically cheated on but i had done the same to her.

She founf out by digging thru my phone, but she doesnt think im all that savvy at this stuff. (None of our devices are rooted) Knowledge is power but pretending to not have that which he does is the most po22werrful of all. Shes deleted her snapchat and she REFUSES to tell me the guys handle, says shes shes never seen a pic of him, but they talked on whisper and snap chat and not one pic? I call BS. Guys if theres anything I can do to get closure please help me. I know its a little weird but I can get access to her phone but not emails due to 2 step verifiication when shes not here, if I can get a stepping stone maybe usb debug could work perhaps an app? ANYTHING I would be greatly appreciative...

Thank you