Fiance Problems

So, my girlfriend has been using snapchat to contact an ex and lying about it. I found a photo of her with no shirt, but only thing you can see is the top half inch of the breast area. It was in deleted pics. then when i talk to her about it and confront her she says that i would get mad if i found out, thats why she hid it. what should i think? also, she broke up with me after i told her i knew she was lying. for months she has been mean, rude, and not herself. like she wanted me to break up with her. i just want closure and to see what you guys think?