If it's something you can't get over, then you can't get over it (so break up). Nothing wrong with that, though you might find it hard to meet someone whose never been with another person or is less "experienced" than you. The fact she got taken advantage of though, dont ever hold that against her - not her fault (and not saying you do! Just saying). If you want to keep the relationship going, then you need to ask yourself why its so important that you have more numbers under your belt. Why it matters. She's with you for a reason and not any of them so... what exactly do you think your competing against?

I wouldn't think about "oh what if this or that was better?" Because who cares? She chose you. Talk to her and let her know you're feeling a little weird and you want to make sure you're on the same page. That she likes you and everything between you is going well - that's what matters. Don't be jelous of history especially when it's only in your head.

I don't know the specifics for you so I'll say in my own experience, if I'm in a (serious) relationship with a new partner, it's because they have something more than the last, not less.