Hey, I really understand why that would hurt. When you open up to someone you love, you expect that trust to stay between the two of you. Having those private things shared — even if she didn’t mean harm — can feel like a real betrayal.
It sounds like you’re not asking her to stop talking to her friends altogether, you just need some parts of your relationship to stay yours. That’s a completely fair boundary.
Try explaining it that way — not as “you’re too open,” but more like, “Some things I share are meant just for us, because that’s what makes me feel safe and connected to you.” Let her know you get that she needs her support system, but that you also need emotional privacy to feel secure.