Boke up with her?

i had just boke up with my gf just bec she was not giving me a good answer about that guy that guy that i saw her kiss him and i took her tell me whats going one she didnt what schold i have done boke up or be with her ? i want her back is that bad i love her so much i bee with her for 4 years like my whole life i am 17 sicne i was 14