When it comes to Intamcy and other relationship problems the key lies between physical and mental attraction. Without those two components there is no connection therefore Intamacy nor the relationship can grow. Sometimes this problem can be solved through communication.
You must understand someones sexual zone you must first enter the mental. If you base your relationship on one thing (i.e sex) then that gets old, your other feelings start to fade away.
At the same time if your relationship with a partner is going downhill don't take it personal because what you want may not be what they want. Don't beat yourself up about it... If the relationship is that important to you just rekindle the flame. Talk about your a topic or subject that intrest your partner, and set up a romantic setting at home or go to the place that you first met or had your first date.... Do these things to remind them of why and how you became a couple.