About the movie

Hi . I have some questions about "Fifty Shades of Grey ". I watched the movie and I read the book , but I don't understand some things .

When I saw the movie , I thought that Christian has loved Ana since he saw her for the first time ,but in the book (Fifty Shades of Grey - told by Christian) it seems like he wanted her just for sex and he tried to seduce her.

I understood that he slowly began to fall for her. With Ana , his nightmares disappeared . And he made things that he said he would never do : he slept with her,he began to have unexplained feelings ..

Here's the question:

Why torturing Ana created pleasure to him ? Why he wanted to do that if he loved her?

I want to explain me all about Christian,please. Have a nice Day!