In Fifty Shades of Grey, Christian " exercise control in all things". The character needs the sex because it's like the only way he can function without doing any damage to anyone. For instance in the book, when Christian has had a long or rough day he needs Ana to come home to . Initially, he wants her to play the role as a submissive and satisfy his needs. We all know Ana couldn't fulfill all of his needs. The point is that sex is a necessity in this movie because that's what it's all about.
Fifty Shades Darker need to show Christian's affection toward Ana and how he worships her body in detail. Like Anastasia says, he always rather have sex than talk because Grey doesn't know how to deal with all of his feelings. Being in a relationship is too new for him. Ana and Christian have made a lot of changes for their relationship to work, but the "kinky fuckery " needs to remain the same.
"Ana you're the best therapy ".
One shade of grey contains his need for the physical touch. Hopefully the sequel has more of that.