Sunshine, if I could go back in time, I'd beg myself to avoid the relationship.
I'd go back to the first time my ex relapsed on heroin. I'd say to myself, "this isn't your battle, this isn't your journey, he's not ready to love you, he doesn't love himself."
I'd go back to when I visited him almost daily in rehab (his fourth of ten stints), I'd say to myself, "you shouldn't visit him so much, in fact, you should rarely visit, he needs to focus on himself, but more importantly, YOU need to take care of yourself."
I'd go back to when he OD'd after his rehab stint. I'd say to myself "I know you haven't heard from him in a few days, but you are going to be OK, he is alive, but this is killing YOU. GET TO ALANON."
Finally, I would go back to the week before I finally left him. I'd tell my then self
"your intuition is right, he is using, you are not crazy, you know what to do. You will do it and you will be okay. In fact, you'll be relieved and FREE."
More importantly, I'd go back and tell myself "run." "Run far away, avoid this relationship at all costs. He will never love you as much as he loves heroin, nothing you do, say, sacrifice will make a difference in his addiction. You deserve better, you deserve a loving, respectful relationship, with someone who loves you. "