Your post is all too familiar ... I love a man, just like you do, who is afflicted with addiction and I stayed by his side for years. AND I continued to keep in touch with him after the (forced) break-up because I still hoped for change. I don't want to discourage you, but here I am, approaching 6 years and NOTHING has changed. It's worse.
Mine was clean and sober 3 years when I met him and very active in our church. He relapsed, began using meth behind my back. Started poppin prescription pills ... (this is about the time I left) and graduated to heroin and crack. Countless jail/prison terms, relapses, detox, rehabs, sober living homes ... Christ-centered treatment programs ... moved cities, states ... jobs ... I could go on and on. I believed him when he cried for help EVERY single time.
What started as natural concern for my partner turned into severe codependency. I became so consummed with his problems, I neglected myself. If I could give you one piece of advice, take care of YOU. Not saying to leave or stay. Pray for him. We never really lose hope, but just take care of yourself, girl ... and know what you're getting into. Addiction is UGLY. There isn't a topical cream to treat it. They say with addiction, you're either using or in remission. It's something that will always be with him, not you. Learn to detach. Go to meetings, see a therapist, read: Codependent No More.
Another thing to consider, I prayed for so long that he would stop using and walk a straight line. He did for a while, several times. What I observed (I am a Nursing/PA student) during our relationship and especially during the periods of non-use is anti-social/sociopathic behavior. He fit every characteristic of someone with ASPD. He was eventually diagnosed with a personality disorder!
I still love him very, very much, but it became no longer worth it for me to be in a romantic relationship with this guy. We could never be normal and progress normally ... like get married, buy a house, have a family. It saddens me too that I can't even be friends with him or keep in touch. All he does at this point is ask for money and favors and attempt to manipulate me - remember I stayed by his side while he was in jail, prison ... rehab ... I never reaped the benefits of this "new" person he was to become. I never saw that person. He is in a very bad place and the only thing I can do is pray for him and be good to ME.
My X is sick, he isn't a bad person. He is in active addiction doing what addicts do. Most new people he meets have no clue who he really is and what's really going on in his life. So sometimes we think we know everything because he "says" so, but watch his actions. Stop being surprised! My X is charming, smart (very!), more than good-looking, he is beyond handsome, funny, talented, brilliant. BUT he isn't any of those things while in active addiction. Right now, I don't even think he has a soul.
Just think about you, take care of you. Work on being the best version of yourself and let him do the same. Protect your heart and remember: Love never fails: It always protects, always trusts, always hopes, always perseveres. Read that last word again: perseveres. You can love him, but can you be WITH him at this point? If you're taking care of him, who is taking care of you?
You can message me anytime you want. Hugs.