confessions of dealing with a meth addict

I'm not to sure why my sister turned to meth
we had everything growing up
from my understanding she has been using since she was 18
she is now 26
and is a roller coaster with the ups and downs
one day she is determined to get her act together
and 3 months will go by with her being sober
however any bad relationship or stress
and she will justify to go and get high
I thought that my support and strength would motivate her to stay on the right path
apparently that isn't enough
we have now parted
she decided to disrespect me and i had my breaking point with her
I told her to leave and never return
she is numb to emotions, or sensitivity
for meth: doesn't care who is hurts, who it uses to get high, it has no common sense
once a person tries it they are forever devoted to that drug
they not the same ever again
it's like deep frying your brain

you can't help someone that doesn't want to help themselves
and amazingly their energy will impact you so it's best that
you show them tough love
and have faith that by mistakes they will learn