Dear star 66,
First we should explore that why she left you?
Is there any misunderstanding between you?
If it is ... then try to rectify.
Once talk to her & tell her that what the situation at that time was.
It is good to have a best friend but the person should be faithful.
Whenever you feel desperate, try to concentrate in prayers.
& pray to ALLAH to give you the best person as a friend.