I would suggest that the problem here has less to do with your ex's past and more to do with your attitude about it.
Being a virgin just means she hasn't had sex yet. It doesn't mean she is more or better of a person, or that she can make you happier than she already does. I find that whenever someone has ill feelings about another person's sexual past, it has more to do with that person being jealous or feeling like their right to ownership has been infringed upon than it does to do with the actual character of their partner.
In all truth, it sounds to me like you don't have much of an opinion about this person at all, and that doesn't really make for a great foundation in the relationship. You say she doesn't enjoy the sex; are you trying at all? Or are you just bringing yourself to the table and helping yourself to what's there with little thought to her pleasure? And I can't imagine you enjoying it much either, if every time the two of you are intimate you're bombarding yourself with images of her having sex with all these other people, which you seem to think is a pretty big deal.
If you care for her, I would tell people to knock it off when they start discussing her sexual past, instead of investing yourself in a gossipy conversation and then blaming her for perceived wrongs. You know her past. Either get comfortable with it, and start being a lot kinder and more open to her, and appreciate her for who and what she is, or else leave her and move on. Neither one of you deserves to live this way.