This story hardly steals from Twilight at all.
The only thing the two have in common is it's about a controlling and manipulative guy who wants to get an inexperienced virgin girl.
But you can say this about lots of books and movies, and this idea is not so original or unique that you can call it stolen, or even a fan fiction for that matter.
After you get past that one idea, the rest of the stories are completely different. Twilight is about a battle between vampires and werewolves. Fifty Shades, is about BDSM in the relationship.
That's two very different things. That's like saying that The Crying Game is a rip off of Tootsie cause they both have man dressed up as a woman. You can take one story element, and say that a whole story is a rip off, just because of the one element in it, where everything else is different.
Unless I am wrong?