I can see your concern. If your boyfriend is particularly large, you may think it certain that pain is in your future; however, a woman's vagina is built to expand for something as large as a baby to pass through. There are a few things I can suggest to avoid the pain that could mar your experience. The first is the use of a personal lubricant. You can usually find "lube" in a drug store or practically anywhere they sell "feminine products" or condoms. Lube reduces the amount of friction experienced during sex and is slick enough to make penetration easier. Second, I suggest that you explain your concern to your boyfriend and ask him to go slowly. You may have to show him exactly what that means, as one person's "slow" is another person's "medium." Alternatively, try different positions. Some women feel that being on top helps them control the depth and the pace of the "exploration."

And by all means, if you start to have intercourse and you just get too tense or it begins to hurt and you want to stop, let him know. It may help to talk about this possibility beforehand, too. There are other ways to have sex until you are comfortable with the idea of having intercourse with him.

Check your comfort level and only have sex when you feel ready to do so. That goes for all circumstances, whether you're not sure about a guy's penis or a guy's personality. Having sex when you're not ready will just make you tense and I doubt you'll enjoy the experience under those circumstances. I also encourage you to have protected sex. Using condoms and protecting yourself will help you relax, as well.