*SPOILERS REQUESTED*

I realize you posted this a while ago, but I'll go ahead and fill you in. It does have a happy ending and Fanny (the dark haired girl and primary character) ends up with Edmund.

Essentially, the film is about a girl (Fanny) who is sent to live with wealthier cousins. She grows up, essentially ignored, and the only one who is kind to her is Edmund. She is in love with him, but he doesn't realize it and falls for the witty but devious Mary Crawford. Mary's brother Henry is attracted to Fanny and asks her to marry him several times. She refuses him because she doesn't trust either of the Crawfords. Her uncle is very angry by this because the Crawfords are wealthy people, so he sends her back to her impoverished family. Edmund comes for her when his brother Tom becomes ill and the family needs her to help nurse him back to health. While there, she is forced to see the Crawfords again, which is awkward. Things become even worse when she and Edmund essentially walk in on Henry Crawford and Maria (Edmund's sister and Fanny's cousin) having sex. Although Maria's married, they've been carrying on an affair. The house is in an uproar, and the Crawfords leave. Edmund realizes he's in love with Fanny, Tom gets better, and Fanny's sister Susan come to live at Mansfield Park.