I think you need to consider the facts at hand. She’s keeping all these gifts and messages from some guy and talks on the phone with him behind your back. Those actions speak for themselves. Don’t think about the good times or how your relationship is unchanged. Doesn’t matter. Definitely confront her about it even if it means she knows you snooped. If she gets mad at the snooping, that’s deflecting. If she doesn’t answer immediately saying that she’ll stop talking to him and throw all of it out, then you HAVE to break up.