If it was that easy for her to leave you over what your “friend” told her about you, she never truly loved you. If she truly loved you, she would have wanted to talk it over with you to get your side of the story.
Her lack of true feelings for you is further illustrated in the fact that she is now hanging out with this “friend” everyday.
Your feelings for her are a lot more profound than anything that she is feeling for you.
You only knew each other for 5 days. Hence, your short-lived relationship had no true foundation.
Given how lop-sided your feelings for each other are, it would be best for you to avoid trying to get her back.
When one person cares so much more for the other, it creates an imbalance of power that will often bode badly for the person who cares more.
The person who cares more could become obsessed to the point of pure desperation and this is something that the person with the power can exploit if they so choose.
It is best to leave this alone and move on.