To "lose" one's virginity is a curious phrase. My first thought is that this phrase implies one possesses her virginity to begin with. To possess is: "to have as belonging to one", "to keep or maintain", "to maintain control over", "to seize or take", "to gain or win". Virginity, for the womun living in patriarchy, is not something to "keep or maintain", it may start off as something considered to "belong" to the individual, but the real purpose of a womun's virginity, within male dominated society, is to be "seized" or "won".
For both men and wimmin in patriarchy, virginity is not something to be held onto or maintained. Men are encouraged to get rid of it fast, this is fundamental to "manhood". Wimmin are encouraged to hold onto it (because of course, if she gives it way too easily she's a dirty shameful woman), but not forever, a man must receive it at some point (because to hold onto it with too much grip makes her a frigid prude, a who thinks too much of herself). To many men, womun's virginity is a prize, something to be won. There can be only one man who gets her virginity, to be that man is to have beaten all other men around the world, something to be worn with pride, like a badge of honour, and military decorations. It is something to "win" by any means necessary.
To lose something implies it was an action taken without the possessors consent. This cannot be said to apply to most men. For the vast majority of men, virginity isn't lost, it's thrown away with fervour, or freely given. To lose something implies that despite possessing it an individual couldn't hold onto it, somewhere along the line it became no longer hers/his. It also implies we don't know where it went.
Many wimmin don't "lose" their virginity, they know exactly where it went, they can remember clearly and with horror the men who stole their virginities. Others, like me, were coerced, either by a man directly, or by society more generally. I carelessly gave it away, out of curiosity and a sense of obligation (after all, what's a seventeen year old high school girl supposed to do when her university-going boyfriend has tolerated her companionship for six months?*)
I do not know the origins of this term, but it is clear to me that "losing" one's virginity is an inappropriate term for the majority of wimmin and men. Moreover, I don't think virginity would be such an important concept outside a patriarchal world. If we lived in a society that didn't see wimmin as sex objects to be competed for, or possessed, if we didn't accept that men are competitive sexual predators (which feminists recognise is socially constructed, not natural), and if we rejected the notion that manhood is bound to preying on wimmin, the concept of virginity would, for the most part, be irrelevant. Virginity is only of import to patriarchy, because the oppressive dualisms between man/womun, masculine/feminine, and active/passive, underlie all social relations.