Well I can tell you honestly, he probably knows that you are a virgin by your actions. If he has some experience then he'll know I'm almost 100% sure.
a)You are not going to know what to do and how to do things properly, what if he wants to change a position, let's say from the side, or from the back.
b)Girls are usually extremely shy, they are very afraid to take their clothing off
c)You probably will not enjoy the first time, it could be seen by the guy.
There are more signs I just gave you the most common. Don't be shy that you are a virgin, I lost mine when I was 21, there is nothing to be ashamed of.