First thing I think to question is are you on any drugs? It can make a huge impact on your sex life.
Like many others will say the key here is to communicate. Which it sounds like you are doing, but sometimes sending mixed messages DURING sex.

Is there any way you can discuss this before you get to the bedroom?
If a man is getting mixed messages during sex it's sending him performance messages like.....what does she want? What am I doing wrong? Have you told him that this issues is based in your brain & not based in his performance. If he feels like he's not fulfilling you it's going to give him a complex & turn him off in the bedroom.

Just my opinion.