<human>: Can you provide a brief rundown of the text in within 3 sentences?

We've been talking via Facebook pretty frequently, and have gone on a handful of dates. We've kissed and shared a bed and done almost everything except sex (and oral sex) I really like her, and I've told her this. She's said that she likes me as well. We're not like, officially together or anything, but neither of us are seeing other people. 

I've had a couple prior relationships, she's had 4. I knew she wasn't a virgin or anything, but I was fine with it. I figured, 4 relationships, some casual sex, maybe about 10 total sexual partners. But tonight we were talking on Facebook, and it came out that she had had sex with 28 different people. To me, that seems like a lot. Like, too many. 

I don't think I can handle being with someone who has had that much more sex than me. Plus, she's 5 years older than me. She lost her virginity before I even knew what sex was. I feel like it's not supposed to bother me, but it does. I feel sick to my stomach. I can't sleep. 

I like pretty much everything else about her, and we seem to get along well. But this just threw a massive wrench into my plans. 

Is this a bad reason to break it off? How do I do that? I don't want to hurt her feelings. Or is there a way to just get over it?
<bot>: the girl I'm seeing (casually) has had sex with way more people than I'm really comfortable with. How do I get over it or break off the relationship?