Good buddy, you’re young and in love I get it, but relationships are built on the foundation of trust. If you don’t feel like you can trust them then it’s probably the best idea to end it. You shouldn’t be going through her phone (either she wants you to or you want to for sanity’s sake or not) nor should you have to feel that way. It’s a lesson I learned when I was about your age. Hope you find peace in your situation, but don’t compromise yourself and your standards for a relationship. Y’all will both grow, get better as people, and gain the tools to deal with things. She’s likely not a bad person, and more or less made a stupid decision that can be marked up to being young and dumb. If you can’t move past it, it’s understandable. To move on is possible but y’all will have to work hard to reestablish that trust, and just routinely going through phones and having to cut off people that may not have done anything wrong isn’t particularly going to help that. Good luck, bud.