Yes, I totally agree - run far far away from this guy, there is nothing good there for you.
There is a book that is often recommended around here, Codependent no More by Melody Beattie. I'm not saying you are codependent, I don't know that, of course, but there is a lot of information in there that you might find really helpful, including information about personal boundaries.
I am also glad that you were able to walk away from the drugs.
This guy is really odd in general, but not odd for an addict. His behaviour is erratic and damaging (to you and to others i'm sure). Yes, you are lucky he left. By now you could be a full blown addict living with some erratic guy, I think you know that is not a life you would choose if you were to really stand back and look at it.
He did do you a favour by leaving, but not really a "favour" - addictions are selfish - incredibly selfish. When an addict isn't drinking or injecting or snorting they are wondering where their next drink or etc are coming from. When they get that drug they are wondering how long it will last.
It's a horrible life and honestly you want no part of it. You sound like a compassionate and nice person.
I hope your counsellor is wonderful, I will be interested to hear what they advise.
I hope you will stick around SR as well and let us know how you are doing.
Oh and so you know, you can click on someone's name (above where their picture is or would be in a thread) and choose to view all their previous threads or posts.