My girlfriend just left me very sudden and I dont underatand why?

I honestly don't know what I'm doing on here I'm just lost and confused. I've been with her for a while and we have had an amazing relationship all around we both seemed really happy I treated her like a queen at all times never did her wrong. 24 hrs ago we were talking about marriage and being a step mom to my kids and even having our own little guy running around. It was a fairytale relationship. I have never been happier in my life. But I took her to her sister's and within a couple hrs she told me she wanted to slowdown and take some steps back because we really are in an awkward position but I agreed and supported her told her I wasn't particularly happy about it but I understood where she was coming from and I was on board and would support her and move at her pace. Today she broke up with me. Told me she was scared and felt like a shitty person because of how we started and that she needed a change. Thing that confuses me is this wasn't how she seemed to feel at all 24 hrs ago. We were literally kissing and holding each other being dumb arguing about who loved who more. It all changed over night. As some back story she did this before about a month ago after talking she said she was scared that she couldn't be dependable enough for me and couldn't help me with bills and be as stable as my ex girlfriend. I told her that I didn't expect those things from her that all I wanted was her love and to have her at my side I could pay the bills for as long as she needed me to. After that talk we went back to being complete love birds but now here we are again and I'm really at a loss as to why. A part of me wants to make this work fight for her again, another part of me wants to just let go I deserve better than what I've gotten and I know that but I'm so scared of losing that feeling I have when I'm with her. I'm lost and confused sad and depressed. I don't understand why I'm here in this position. I know she loves me but I don't think she cares about me.
My girlfriend just left me very sudden and I dont underatand why?
Post Opinion