Guys, I haven't been around here in a long time, but I happened to come by thinking about this very same issue. It took me a couple days to remember my password, so here I am again. I stopped coming around because I got into a relationship and just got too busy for the distraction after a while. Plus I was trying to stop messing around with girls on the side and you guys made it tough!
I've been with this girl for five years now and recently found out some things about her past that upset me, too. There is definitely a difference between suspecting things and knowing details.
My advice on the numbers: don't ask. Don't even bring it up. Too much talk about this shit destroys relationships and, most importantly, disturbs your inner peace and sense of balance.
The caveat is this: Do whatever you want if you don't plan on having a relationship other than banging it out or pump and dump. But, my relationship started with a somewhat random hookup and yours might, too...
If you want a future, you don't want to have pictures in your head of every dick that's been inside your precious piece of pretty pink.
Remember, every person's life is different. If we start off with a rigid list of requirements that no one can live up to, we'll never be happy. That said, every one of us should have some requirements that we absolutely do not compromise on.
So, I've been going through this history thing in my head for the last few weeks. It started with a couple of accidental revelations that really shook me up, but in the end, I had to look at the whole picture. I'm with this girl, we have been through so much shit in these past years with lost jobs, money, drinking, my father dying, trouble with kids and exes. We've come through all of it closer than ever. Sex is and always was porn quality and frequent enough that most guys my age would be shocked.
I've seen her change herself for the better over the last few years through sheer willpower and it blows me away what she's overcome. During this time I've made myself better, too.
My situation may not be the same as everyone else's, but here's the bottom line:
Happiness in life is so rare and so fleeting, that you have to put all these things on the sides of a scale and see what's most important. For me, I have to let it go and move forward.