Reminds me of The Lost Weekend
I was just watching Billy Wilder's The Lost Weekend and thinking how much this movie resembles it.
A heroin addict/alcoholic guy trying to maintain a relationship with a girl (named "Helen" in both movies), living off his brother, being recluded in an institution, pawning things and eventually stealing to get more drugs/alcohol... It's funny 'cause this is the movie Al acted out when he was a kid.
I think when it comes to movies about addictions, these two top my list.
My Godfather tribute:
http://www.youtube.com/watch?v=sg-YnQHH9ZY