Michelle and Sebastian = Sid and Nancy
I couldn't help but compare Michelle and Sebastian to Sid and Nancy.
Michelle always whining or freaking out and was the main source for getting the dope.
Sebastian, young and dumb like Sid and has a violent fit where he beats Michelle on the street. I can imagine that Sid stabbing Nancy was probably the same small kind of provocation.
And lastly....a heroin addicted couple in New York.