It is so hard dealing with the addiction of someone you love or have loved.
I try to tell myself it’s not my husband when he uses, that he is a different person while under the influence. It helps me a bit with separating the addicted person from the person I love. It has gone so far that I even made up a different name for him while he is under the influence (I’m not suggesting you do the same, I have no idea if this is unhealthy or not, I’m just sharing my weird coping mechanism!). I feel truly sorry for the addicted person, and I get very angry and sad when I see him. But when he is sober I try to not show pity to him, but I do try to be understanding while he is still taking tiny steps to do better (like continuing taking his meds for his depression).
You have to continue to remind yourself that what he does is not your fault, the fault is his and only his. While he doesn’t do anything to get real help, it’s all on him. My husband tried blaming me when he was at his lowest point, saying I wasn’t hard enough on him, and didn’t monitor him enough?? Ridiculous. He has since owned up to his faults, he did that when he started on his medication for the depression.
I truly hope your ex sees the light and gets the help he needs. This is such an awful situation he has put you in.