Hi Wing,
I want to say firstly that I understand all the things you are doing and feeling and I hope that things will get better for you.
I do agree with Windmill that if this guy is your ex you need to focus on your needs not his issues - easier said than done and maybe not what you want to hear at the moment.
Relationships end for all kinds of reasons but I can imagine that with an addict you feel if you can find the answer you can put everything right, but there isn't any one true answer.
I have a BF who has an addiction we are currently still together and he is in recovery. As soon as I decided enough was enough but still wanted to stay with him I realised I had one choice and that was to live my life and hope that he wanted to live his enough to take care of his recovery. Our relationship may not last but I work each day on understanding that I can not sacrifice my quality of life in order to save his. No matter how knowledgeable I can become on addiction I cannot control his recovery only he can do that. He had all kinds of horrible thins to deal with as a child - abandoned by parents, abused in the care system but as an adult he needs to have learned how to deal with the demons and not use them as an excuse to get high and blot out life - life can only get better when you actively choose to take control of making it better.
I believe you need to concentrate in moving forward and believe in a time when you won't be hurting as much and you can help that happen - do things for yourself, remember the things and the people that make you happy and seek them out. You are not failing by letting go of him.
Here are a couple of mantra’s that are getting me through my tough days:
• You cannot control the thoughts, feelings, actions or words of others
• And nothing is the end of the world
I wish you the best in your journey.