so I need to know why this happens..and please dont assume something without knowing or experiencing this yourself.

I tend to dry up during sex even in the heat of the moment,or shortly after I have climaxed. My boyfriend thinks it's because he gets to rough..maybe so but I actually like that. I notice it happens a lot when I am dehydrated or have been drinking before hand as well...so I don't know, I just dont want it to affect our sex life. Other than this issue- it is fantastic! but he thinks when this happens he's hurting me..and then he goes limp. which makes me self concious even knowing the circumstances.
do we need lube?.. maybe we should slow down during sex?..I think we also need more forplay.. any advice?