The Panic in Needle Park (1971) on Netflix

This movie is a stark portrayal of life among a group of heroin addicts who hang out in "Needle Park" in New York City. Played against this setting is a low-key love story between Bobby, a young addict and small-time hustler, and Helen, a homeless girl who finds in her relationship with Bobby the stability she craves. She becomes addicted too, and life goes downhill for them both as their addiction deepens, eventually leading to a series of betrayals. But, in spite of it all, the relationship between Bobby and Helen endures.