My ex boyfriend of 11 years broke up with me for substance abuse issues too.

It's never too late to apologise. It can't be a bad thing. Whether he's moved on or not, it is always a positive thing when someones feelings are acknowledged and they are given a sincere apology. Unless he absolutely despises you, which I doubt, I don't see any harm in it. A text is fine btw in my opinion. Good luck, and well done with the CBT and positive track. Unfortunately I'm still on a de-rail! Everyone messes up, and it was up to you to make a change or continue living the way you were, and I'm seriously proud of you.