@angelica1205,
I agree with Cylco.
But to answer your question... there is a basic rule of relationships: You don't start a new relationship until you have resolved (i.e. are completely through with) the old one. This guy has clearly not ended his old relationship-- and at the very least, you should not back out until at least this old girlfriend is done with.
That being said, the big red flag here for me is the addiction to narcotics.
Unhealthy relationships are common with drug addicts where they find someone who will "support" their habit by protecting them from having to deal with it. If you read about any drug treatment program (i.e. al-anon) you will see that dealing with these relationships are central to treatment.
It sounds like this guy is tied up in this type of relationship-- and trust me, you don't want to have anything to do with this.
Probably a healthy romantic relationship with this guy is simply impossible-- he is simply not ready.