Sincerely, I can't say you should just give up but you should first seek God's guidance over your relationship affairs. Some things doesn't last not because they are totally bad. But because there is a better purpose in your life. I understand your pain and I trust to know how it feels. I was once in same shoe, when the lady I was dating actually said same thing; on that very day, I became shocked and disbalanced. We actually met sometimes around 2008 and love started and trust me, it was fun that I never want to miss a moment. Suddenly she started giving attitudes and distance, I tried to check but she always refused me, did I remembered to tell you I was actually into a relationship before I met her. And I had to plead with the first girl I was with to let me go since she was not actually serious with me then. So it working fine with us, till she started acting.
As at when she told me she want to quit, 8 thought I could still buy her heart back.but I forgot that "no woman quits for no reason, its because she get new guy". All my efforts and prayers were in vain. I later gave up.
Few years after then, she got admission into my school and she started hearing my name everywhere for good. Then she started by sending text requesting to see me. We met but by then I was already into a better relationship relationship. She started feeling jekouse and bad about her past. I encouraged hher to move on. It was until this time that I knew what God actually took away from my life in the past which might be being my forever regret till today..
So, if you try your best and it didn't yield, please let her go.