Need advice to help my gf

People who have dated / loved someone with bpd, i really need advice. My girlfriend and i are both in high school and she has bpd. We’re extremely close and she trusts me a lot with how she feels. Sometimes she feels stuck in mental loops where she thinks nothing will ever get better. During this easter break we had a few days off school and she said it just showed her how miserable her summer is going to be. She also says when she looks back at old notes or videos she feels like she reacts the same way every time and hasn’t grown at all. I try to stay hopeful and just be a stable presence for her and remind her she isn’t alone. For people who have experience loving someone with bpd: what helps when they feel stuck in those loops. (This is kinda just scratching the surface but i will go more in depth if needed)