What do i do if one of my friends hates me now?

One of my friends ex-gf used to be one of my friends i used to think she waz a stuck up gurl because all of his old gfs all were but she was different so we became freinds i used to sit with her durin breackfest and lunch cuz she wanted me to now she doesnt tell me what i did to make her mad she acts all mean to me now iwhen i dont think i did nothin wrong