Zuwulguu uguuch pls

I have been dating my gf for 9 months. We were doing just fine. But then she just left me. This happened to me twice. Just when I think to myself that I found the one, they leave. Without her my life feels empty. She turned herself into a part of my life so she can just leave. Why do they do this? I always asked her if I make her feel enough, she always said yes but it was a lie. She promised that she will not leave me. But she did. Why do they always promise if they cant do what they promised? I am genuinely at my lowest rn, I js need some tips on how to get rid of the feelings that get more and more hard to cope with day by day.