In the Spiderman movies...?

In the comics at the time the first movie was released, Peter Parker and Mary Jane were in a long-term relationship (i.e. married). I think the decision to have MJ as Peter's love interest in the movies was based more on that than anything else. If someone who saw a Spider-Man movie bought a copy of a Spider-Man comic book expecting to see him in a relationship with Gwen, their first question would have been "Who's the red-haired chick?"