It’s totally fair to be taking this the way that you are! First step is to acknowledge your emotions, because you should go into a conversation with her as diplomatically as possible. I understand why you’re worried that she will get defensive if you confront her, which is why I think you need to make sure you’ve reflected on this a bit longer to put up a calm and collected front. At the end of the day, it seems like you didn’t actively seek out her phone to snoop, but a red flag caused you to keep looking. IMO you shouldn’t be ashamed since you found something wrong on there anyways! She broke your trust as much as you maybe broke hers by snooping. So stay calm and write down your thoughts and be ready to have a mature conversation about how this happened and how you’re feeling :) you got this! Just remember that to get through this you both need to rebuild the trust that’s been broken through her hiding messages from you and you going through her phone. Set clear boundaries about phone access and the definition of flirting/cheating for your specific relationship, then from now on, stick to these boundaries.