The non-addict girl is a girl who picked up heroin while you were away. So she still does need to go through a long period of personal growth and change before she could be ready for committed relationship. People pick up heroin for a reason. Until she is abstinent for a year to three years and matures through counseling and work on her underlying issues in sobriety, she cannot be who you need her to be. The heroin, the rehab escape, both are symptoms of a deeper matter which must be addressed before she can meet you as a whole person who is ready to be a partner in life.
It is your choice to step back and wait, or you may wish to let go entirely. But if you decide to wait and see how her life unfolds and how that affects your life and whether there is hope for reunion in a year or two, I suggest you enter counseling so you do not sacrifice far more than you should. I know what it is to wait and see, and had I not been in counseling, I think the waiting would have made me quite emotionally ill, as my entire focus would have been on the other person. I had hard enough time with self-focus even with Al-Anon and counseling. We hold such hope, we have such longing, and we are simply unable to change the reality that the addict is too self-absorbed to care for us. It is very painful.