2 weeks of not even seriously dating and you went through her messages? Mad sketchy.

I'm just gonna put something out there that's going to be an unpopular, disliked fact. Girls tell their best friends EVERYTHING. Good and bad, ESPECIALLY bad. My best friends know disgustingly intimate details about the sex I have with new partners, and more. They know that I dated a dude for 3 months who gave me the worst sex of my life that I constantly complained about, but I stayed with him because I loved him as a person. That's just how it is. We sometimes also talk shit about guys. It's usually harmless, and comes from a place of making bad jokes in times of uncertainty and anxiousness in the relationship, like when you're fighting (or maybe possible when the dude is unsure about getting serious with you and you're bracing yourself for the breakup, just a thought). I'm not saying it's right or that it's a nice thing to do, I'm saying it happens.

Its not cool that she was saying shit about you behind your back, but I also think it was messed up for you to go through her stuff so just stay broken up because she needs someone who won't do that to her after 2 weeks.