I know how much this hurts you Lucie. I am sorry you are going throught this pain. My daughter (21 yr) is the addict in my life. She has a younger sister (18 yr) who has been experiencing probably the same pain that you are now. What helped my youngest daughter was what we call "the three C's".
We jut kept repeating this phrase over and over again. I didn't Cause it, I Can't Control it and I can't Cure it.
What we have learned her is to take care of ourselves and turn our addict over to our Higher Power.
HUGS to you and keep posting here. There is a wealth of information from these great people here.