How is the fairytale The Little Mermaid different then the movie?

The fairytale and the film are different in a variety of ways. One of the "huge" differences is in their conclusions. In the movie, Ariel and the Prince live happily ever after. In the tale, the Prince marries someone else.

And the little mermaid lifted her clear arms towards God’s sun, and for the first time she felt tears. On board the ship there was noise and life once more, she saw the prince with his lovely bride searching for her, sadly they stared at the bubbling foam, as if they knew she had thrown herself into the waves. Unseen, she kissed the bride’s forehead, smiled at him and rose with the other children of the air up onto the rosy cloud that sailed through the sky.