Opinions on this?

Alright so i heard that my "Bestfriend "went to see my ex boyfriend knowing that he did me dirty and I cried to her multiple times about this boy. Even cried the day before she was supposedly with him.They was parking lot together and she was laying on top of him. ( my Bestfriend sleeps around btw) but I wouldn't think she would do this to me. Only one person was there and confirmed it was my Bestfriend . I asked her and she keeps denying it . She goes through a lot at home like her mother doesn't want her at all and she doesnt have any clothes but now I don't feel bad for her if she does this shit to me. What should I do? I can't text the boy either cause he will probably lie and I've been blocked.