I found out something about my sister last night and I dont know what to do with the feeling it left me with

This is messy so I will try to keep it simple. My sister and I are both in our late twenties and we have always had that weird mix of closeness and distance that happens when you grow up sharing a room but never quite the same world. She was always the more confident one, louder, prettier, the one that people remembered. I learned to take up less space without even noticing. It is just how we were.

Last night we were at a small family dinner at our moms place. Nothing dramatic. Pasta, wine, everyone talking over each other. At some point my aunt started telling a story about when my sister was sixteen and sneaking out to see a boy. Everyone laughed, my sister rolled her eyes and said something like yeah yeah those were the days. But then my mom said softly I was just glad you finally felt safe enough to come home and that sentence hit me like a truck. Because I had never heard it before and suddenly the room felt different.
After dinner I asked my mom what she meant. She hesitated for a long time then told me my sister had been struggling back then way more than any of us realized. Anxiety, panic, some awful stuff with kids at school that she never told me about. She said my sister used to sleep in her car sometimes because it felt safer than our noisy house. I just stood there, stunned, because I always thought she was the strong one while I was the fragile one. And now I am realizing that maybe we were both breaking in silence without knowing about each other at all.

I went home feeling guilty for not seeing any of it, and sad in a way I cant quite name. My sister and I talked for an hour today and she told me she did not want to burden me back then, that she was trying to protect me. Which only made my chest feel tighter. I do not know what I am supposed to do with this mix of love, grief, and something like helpless anger. I guess I just needed to put it somewhere because it is sitting in me like a stone and I am scared to drop it on anyone in real life.