Based on what you said, yes, I think she was trying to clean the slate with you. I don't think she's going to expect you to take this in 100% full stride either.

Sans mentioning the physical reaction (not to lie by omission, but I think you're in the inconvenient situation of if you do mention "it makes me sick," it's going to be perceived as a cliche insult over what actually happened), why not talk to her about this? Explain how you feel, ask why...etc etc. I do agree with Leed in that she (and, not to scare you, you, if you two have been together) should get tested.

I am forced to wonder though...what was her childhood like, do you know? Losing her virginity at such a young age coupled with the high volume of partners...to me, it hints at a red flag of some sort. Does she have a record of any type of mental illness such as depression or bipolar?

I think her "offhanded mention" was her compromise to herself on coming clean to you while trying not to make an overt issue of it. I don't think this is something she would mention if she didn't feel remorseful about it and didn't seek...not your approval, per se, but...I think she needed your recognition of the fact that it happened and your acceptance in spite of it. Keep in mind, her ex husband is likely going to die (which I might add, I am sorry to hear ). Even if she doesn't love him now, she did, and there's always the issue of breaking it to her son. She probably isn't in the best of places right now.

For now, be supportive of her and her children. Please try to give this some time. This was an offhand mention. You don't have any facts aside from that it happened. You don't know why, how she feels...anything like that. That may help sway your mind one way or the other.

At the same time, your feelings are understandable, and I wouldn't fault you for them. But I think it is in your immediate best interest to get all the facts that you can and have an open dialogue with her on how you feel before you do anything.

Please take care. Know I am praying for you.