My boyfriend and I barely have a sex life?

We've been together for 4 years. I'm 21, he's 24. We live together. He had a very active sex life prior to meeting me and we were pretty active in the beginning but for the past year or so it's just been shitty. The sex doesn't last long, he's not putting much effort into making me feel good, and it only happens MAYBE twice a week. I crave sex and I want that passion with him but it's not there. I've talked to him about this before and he says he just isn't as sexual as he used to be. But sex is so important in a relationship. It's gotten to the point where I just feel bad about myself when we have sex because it becomes all about him. I don't know what to do anymore.