My friend was raped by he ex-boyfriend?

My friend had been in a relationship with this guy for a year(My friend is 13 by the way, she is just a teen) they were in this relationship and toward the end of it something just seemed off but no one knew why. after they broke up she told me that he had forced her to do things to him and forced sex on her four times. Every time she talks about it she cries and I am really worried for her future. He continues to give her guilt about leaving him but she is staying strong with me at her side. She told me not to tell anyone but I don't feel at ease with the whole subject... what should I do? (I am a 14 year old teen)