Afrin,

In my perspective, God has realized that ur friend's love is true, but the guy is not worth for it.
So, she has been provided with an opportunity to correct her mistake.
Her decisions should be wiser from now onwards.
She should spend more time with family and friends. She should not be alone which will put her into more depression.
She should not accept the guy, if he comes back for any reason.
This is not the time to fall in another relationship. some people fall in another relationship because they feel that would help.

Is your friend is sure that her BF has left her for the reason that u mentioned in ur post?
sometimes, there might be untold reasons for the welfare of ur friend. (poor guys thinks like that too)
of course, failing in love is a biggest tragedy in life. only the victim could feel the real pain. so advising cannot help unless she wants to overcome from that.