Hi MissWestCoast,
I agree with Maudcat, I would leave him. I have two family members who shoot heroin/ have a heroin addiction. It has really taken a toll on their lives as well as family members' lives.
It sounds like you're not married, have no kids, and he isn't even always around. Seems like you give yourself (and him) a clean break and move on with relatively little complications.
Best of luck.