Mi best friend is dating a complete *** ! HELP ?

she has been going out with this guy let call him jack Jack lies about him being rich and him being a model and childish crap but recently acouple of me and mi mates saw him getting off with a gurl hoo goes to the school down the road we decided to tell her she dumped him she went back out with him but 2daysa go we saw him with another girl out of school and dont no if we should tell her again because she had break down last time and i no its not mi life but She cant be with him because he is awlays putting her down and lying and she desrves better wot do i do ??