How do you get a girl to breakup with her boyfriend without hating you?
You did not explain whether you wanted to get her to breakup
with her boyfriend for your own gain or that you didn't feel her
boyfriend was treating her well and you're just a friend and
concerned about her. If you are a girl then perhaps you have an
alterior motive? Leave well enough alone and even if you succeeded
in breaking them up she would go onto someone else and if she ever
found out it was you that was the cause of the breakup you'll be
history. Even if she is not being treated well, you don't like the
guy or you're a woman wanting her boyfriend you won't win!