Well, me, I left my ex because he used and wasn't willing to stop. But that's me. My own personal boundary is that I won't have active drug use in my life and I frankly don't care what anyone thinks about my boundary.
In your case, it sounds like you are ok with active alcohol / drug use in your life, yes? And if you are, then why would you pay attention to friends and online strangers who have an issue with drugs / alcohol?
But if you aren't ok with active alcohol / drug use in your life, you would be doing your ex bf a disservice by telling him that you want to rekindle things while having a hidden agenda. You would also be setting yourself up for continued heartache.
Sounds like you're looking for someone outside of you to tell you what to do / give you rules. These things should come from within.