Have we lost our feeling?

Does anyone not enjoy having sex with your SO? We have been together for 5 years and we used to enjoy it all of the time and now I never initiate it. If he does and I go with it I eventually get into it, but when he brings it up I really don't want to. He doesn't force me into it ever though! 
​I'm worried I'm not attracted to him anymore. Or if our love has fizzled. I love him with all of my  heart and never want to be with anyone else, he is definitely the one for me. 
​Note: we have lived together for one year and are 20 years old. 
​Help!!!