I M23 went through my gf 21F phone and found some messages that have been bothering me. How to proceed?

To start, yes I know I shouldn’t have went through her phone, but something was telling me too. I trust her or did trust her so it wasn’t cheating I was worried about.

Anyways, we have been together for a year and when we first started dating I expressed that I don’t like when relationship problems is spread around to family and friends.

So, when going through the messages I found out that she tells her sister most of the problems we have. She also allows her sister to call me names.

Along with the arguments she is telling I found that even when she isn’t upset about it anymore they say things like “milk it or pretend you are upset so that I can pay or gift her something. She also left remarks like “I don’t even feel bad for how I’m doing him.”

Another big thing is I found that she took pictures of one of my medications and told her sister about it (mentioned the name but did not send a photo of it). The medication isn’t anything crazy either nothing sexual etc.

This has really hurt me because I did/do see a future with her. I don’t go to others with our problems out of respect for the relationship and the both of us + if she gets over the argument family and friends can still hold a grudge. And I would never allow others to call her names.

How to proceed? I have not brought these things up to her yet.