^ I gues you're not expected to if it's the first couple times. But if you've slept together more then.... let's say 3-5 times.... then you should be comforatble enough to tell him. You don't even have to tell him, if he's good at a certain position or you like it a certain way with him then make an attemp to get in and stay in that position. You can always ask him to slow down or speed up, guys like that.... or HARDER, HARDER, FASTER, FASTER.... hehehe
