WAS i wrong to cut ties with a bestfriend?

i met my best friend through my brother(my brother's g.f). we've been bestfriends for two years.my brother treats her like trash.he cheats on her beat on her and call her all type of names.she constantly runs to me a cry on my shoulder and tells me its over but always runs bck to him.her son calls him his daddy but hes not a role model.i recently told her about this girl dat my brother was messin with.shes turns around and told him i told her and now my brother cut ties with me and told me im two faced.so i no longer wanna be a friend to my ex friend cuz of dis and depressin spirit she carries around her dat effects me. her and my brother continuisly fist fight ang give eachother scars.and im tired of her running back to me crying and saying nomore and when i look around shes crawling back to him.and the incident happen more than 20 times.am i wrong to cut ties with her?