Girlfriend and her ex?

Sorry if this is long but here’s a run down. My girlfriend F18 and I M(17) have been dating for 6 months and known each other for 10 months. We know all about each others exs and stuff for obvious reasons. The other day she brought up the fact that her ex unadded her and was very disappointed, to which I got a bit annoyed at the fact she was upset about it but she later claimed it was just a joke. She has recently left for a couple of days for a holiday and asked me to do TikTok and Snapchat streaks for her. Now I made the mistake here of snooping a bit through her TikTok (I take responsibility for that it was immature) where I found a conversation between her and a friend where she confessed to asking her ex about a question she had regarding MY AND HER s*x life. I was confused because she said he only reaches out to her occasionally and they never talk, so I scrolled a bit further down and low and behold she had just recently blocked him across numerous accounts, but in the chat history she was clearly the one reaching out to him every time. So not only did she lie but she was talking about very private matters with him. Furthermore, her best friends bf is also doing her streaks, and as we started talking on each others gfs accounts, I saw a recent saved in chat of me. It was a photo which she had taken a photo of on another device so I wouldn’t be notified, without my permission and sent to her best friend which she laughed at as it was an embarrassing photo for someone else to see. My birthday is soon and I really don’t know what to do please help. How should I handle this situation?