There are plenty of things to fight about in relationships without sex getting in the way. When you have to face conflicts about trust or commitment or intimacy --as we all do in relationships-- getting out of sorts about your girlfriend or boyfriend's number of previous sexual partners is something that you really don't need to do.
Unfortunately, though, you can't always prevent it. Because you don't set a cap on the number of sexual partners a prospective date should have been with on your internet dating profile, you're not always going to be able to predict how your experience will compare to that of somebody you're dating. You can't always predict the way that their "number" will make you react. Nor can you know how your partner will react to your own number. It can be a delicate discussion.
But there real question is... how many is too many?
What it Really Means
Of course, the answer to this question varies from person to person: the idea of "too many" is strictly your own. Ideally, no number would be too high or too low, and partners would simply accept each other for who they are and what they've done. But we don't live in an ideal world. So we have to think about what "that number" means to us, whether it be our partner's number or our own.
While a person's number of sexual partners is meaningless on the surface, it does give some indication of their perspective on certain issues. For instance, if you've had many sexual partners and your partner has had very few, it may be an indication that your values and perspectives are quite different, both emotionally and morally. Not to say that any person's values are better or worse than the others... just that there may be some issues with compatibility.
The thing you should really look at when deciding what you or your partner's number means? How you both behave now. What you or your partner did in the past might be an indication of how you used to look at the world; but how a person behaves now is an indication of who they are at this very moment. And which, really, is more important?
Who Should Worry About It
The truth is, nobody should spend too much time worrying about how many sexual partners they or their mate has had. Why? Because having sex with a particular person is only about how that sex is with you. Who they may have had sex with in the past has nothing to do with your own sex life. Sex is personal, it's private, and it's only about the two of your together; if you let other things get in the way, you're shortchanging your sexual relationship.
However, there are some parts of a person's sexual history that might affect your current relationship. If somebody you're dating has an STD or a history of STDs, for instance, their sexual health and your own should be a concern. It's a good idea to be sure that they're checked out (and you are, too) before getting intimate. You might also want to look at their (or your) behavior itself with their different sexual partners. Did they have a certain number of partners because they tended to cheat when in a committed relationship? A history of cheating may tell you something important about your future that their number of sexual partners will not.
The truth is, the number of sexual partners somebody has had means very little. Everybody had different instincts, different backgrounds, and makes different choices. Worrying about how many sexual partners you or somebody you're dating has is simply something that society tells you to do. And there's no way to please society. After all, what is a conservative and acceptable number of sexual partners to one person may qualify as "slutty" to another. You can't win by trying to follow society's artificial rules about how you "should" look at sex. All you can do is follow your own.
And that's where the solution lies. If you or your partner have very different "numbers," it's understandable that it may be a concern. But what's important is how you feel about it, not how society might look at it. If your partner's number seems too high, it's important to look at why you feel that way, and try to come to terms with your issues. If your partner considers your own number to be too high, you can't let their issues with sex affect your self esteem. You have to work together to keep from letting these differences come between you.
We all have to make choices, sexual and otherwise. Nobody can make those choices for us, and so nobody has the right to judge the decisions we do make. Everybody's experience level is different. It's important to try to learn from your different experiences rather than let them come between you.