Agree with OGRastamon and Whtspt -- 2 intelligent responses.
Add: It's sad that puritanical social thinking and religious endoctrination—over many hundreds of years—have instilled in minds of many younger men such a senseless obsession with whether their girlfriends are "virgins". In this era of greater enlightenment—which allows one to think logically and not just accept things simply because "it's always been that way/or believe what you think society says." Intelligent people, in modern times, get past obsessing over whether their girlfriend is a "virgin."
As posts accurately say (above) ... it's near impossible to know in most cases—other than by doctor evaluation. P.S.: Any girl asked to have such an evaluation done by a wanna-be boyfriend should dump him just based on that alone: the combination of distrust combined with stupidity makes for horrible boyfriends!
As the 2 posts mentioned accurately observe: If your girlfriend has had sex before—and so long as she is free of STDs (sexually transmitted diseases)—then you are probably both better off. Better off in the sense that: your "sex life" with her will probably get off to a better start for both of you.
The primitive, animalistic notion of a very small number of men might make some think the idea of being that stud that gets to "break the cherry" (rip the hyman, hurting the young girl with his "big member" and making her cry and bleed) is erotic (turns them on). But, as I prefaced it: this is so primiative and animalistic to think that way; if that is more than a passing fantasy, you might need to see a sex therapist if you have such sexual desires (it might even be the seeds for becoming a sexual predator). The theory of sex with a virgin being special is purely theoretical; in reality it is usually not a very rewarding sexual encounter for either party!
Also as Whtspt suggests:
I agree, it is GOOD IDEA to both get tested for STDs prior to having a sexual relationship if you want to be safe and if there is a possibility of prior sex (or known prior sex or just as a matter of course) and if you intend unprotect sex.
That is a FAIR AND REASONABLE REQUEST for a potential sex partner to request the other to be tested for std's before taking a relationship to sexual. It's ok to DEMAND testing. I dated an intelligent, younger college girl recently and she DEMANDED I have std testing and she wanted t