I agree that you should let this guy know. If you guys can't talk openly enough about something as that, then I don't know if you should be having sex.
And like Tease said, if he doesn't know....then he won't know to take it slow and easy and end up hurting you bad. Then when you yelp or bleed, then he'll know you are a virgin anyways, most likely.
I didn't bleed, but I was sure glad my b/f took it slow and easy. It took a little bit to get comfortable with him inside me.

I'm with Tease. You need to tell him and expect him to act accordingly. Just because he's been with other women doesn't mean he knows your body. You have to learn the person you are with at the moment.

Take care and remember to play safe (use condoms).

Well, you really might want to tell him.
If he thinks you're experienced, then he's probably going to act like that when you actually do do it and he would probably go rougher than your body is willing to accept.

The one thing I will never forget about my guy is the fact that even though he was experienced, he knew that he was my first and we went slow. If I told him to stop, he would stop. He would ask me, a lot, if I was ok. And even if I didn't tell him to stop, he could see it in my facial expressions that I wasn't really "ok" and he would stop and we'd try something else.

I think it's very important that your first be a lot like my guy. Understanding and caring enough to get you through the experience. Most girls first times aren't pleasurable and personally, I'd rather have a painful experience with a guy who was caring and understanding than a painful one where he didn't give a crap about you and dove right in.