Loving someone enough to let them fall

Maybe I've written before about this..I don't know. A person that I care about deeply is addicted..not to a substance but to a person. I see her getting pulled down by attaching herself to someone who does not return her love...to a person who is an addict himself and only dragging her down with him. She believes that she has point where she will say "no more" but that point is really far off in the distance it seems. I worry sometimes that she will hurt herself in the meantime ..hurting herself to a degree that she cannot repair so easily...yet...she is an adult...she is fully a person in her own right and can make her own decisions. It hurts me to see her go through this but I can't avoid her either as I am one of the few that will listen to her woes lately. I don't want to leave her without anyone else to talk to...so I guess I am sort of stuck here...trying to trust that all will work out for the best...but still trying to keep out of it and let go.
I can pray...at least I can pray.