Okay, this is what I'm going to say. It's really easy to want to try to control things. You may want the best for someone, but that's still wanting something FROM them.
I think my biggest mistake in my relationship with my ex is that when he told me that he was an addict, years ago, I didn't know much about it. I just said, well okay, just stop using drugs then. I said you will prevail, you are strong, you can be whatever you want to be... blah, blah, blah. But he DID say, "Okatz, I am an addict." I. AM. AN. ADDICT. He didn't say, "Okatz, I want to go to rehab." He said, "Okatz, I am an addict." Then he heard me say (for years), "don't worry, you can get over it, you can stop." So in his mind, he thinks, "this woman doesn't really listen to me... and she buys me stuff... she's not listening to me and she's a malfunctioning ATM... and cook... and cleaner... and nurse. She's oblivious. I can work this! I can have a normal life, a normal relationship, and ALSO use drugs. I can use drugs and be NORMAL! SCORE!" This is probably not what he was literally thinking, but I'm sure that deep down inside, it probably went something like this. I think this is when he started lying regularly and the lying became a snowball that nearly killed both of us (and probably will kill him eventually). I didn't listen to him.
I look at my family of origin and my parents were "fixers". You did something wrong? You have something wrong with you? You feel sad, angry, uncomfortable? Let's fix it. You can't afford something? Tie a bunch of sticks together with duct tape and Mcguyver it. We were the opposite of Wreck-It-Ralph. We fixed things. We tried to fix people. Meanwhile, my father has not had a vacation for the past 10 years. You are in grad school? I was too. People who are high achievers often do not take no for an answer -- not from themselves or anyone else. They find it hard to believe that they can't "fix" something. They want to understand everything. But human beings are not a PhD thesis. Being able to intensely focus on something outside yourself is useful when you're writing a thesis (you forget to eat, you drink too much coffee, you barely sleep, just to get the work done), but it's a totally useless skill for relationship building.
I am now only stopping and taking stock of the mental issues that brought me to the point where my qualifier almost beat me up and then became a hobo (for a time... although who knows if he didn't have an extra woman waiting for him to move out of my house? Because I did not tolerate or hear his truth: he could not stop the drugs... he also did NOT want to). It didn't have to get to this. I didn't have to stand in his way and fall in love with the reflection of my fantasy life that I saw whenever I looked at him -- it was like I was looking not AT him but at a mirror, in which I only saw what I wished FROM him. He knew this... in some way he must have known this. How small it must have made him feel. How little he must have valued himself that he accepted this from me -- I was a person who did not see HIM when I looked at him. So he did not respect me. He could not. I suspect this is why your ex doesn't respect you either.
The more you want something from your addict partner, the more you risk provoking a build-up of narcissistic rage, because you will be asking for more than they can give. From the addict's point of view, you are asking them for things that are unreasonable -- for them to be sober is unreasonable. For their families and friends and loved-ones to NOT accept their choices/need to drug/drink, is actually rejection of them. They feel rejected. They feel that the reasons for their addiction are dismissed by you, who wants them to "go to rehab". While they resent that you don't see them for who they are, they don't want to see themselves for who they are either.
I often wonder if by loving my ex, I made him sicker. I think in some ways, I did. I made it possible for him to avoid responsibility. I stuck by him. I should not have.
I know how much you miss her. People go through so much pain on both sides -- it's just that your ex numbs her pain, you wallow in it. I don't even post pictures of our formerly shared pets on social media because... it would be cruel if my ex saw it. It's better for my ex if he just disliked me enough to move on with his life (but not so much that he had a vendetta). I want him to be happy. I also want him to be healthy but these are just fantasies. It's good enough for him to just be happy. If drugging himself into an early grave is going to give him happiness, well.... I love him enough to say he should do what he wants with his life. I mean, I'm out of the picture, he can do what he wants now without someone worrying about him. It makes me sad that he might continue using drugs way into his mid 40s (if he even survives that long). Nothing I want to say to him will be heard by him. Nothing I have said to him was ever heard by him. I can't even say goodbye.
It's very hard to let go. I let go when I had nothing left to hold on to... except hope, which was dangerous. I hope you don't wait that long.