OK she is my first girlfriend I ever dated. I already had sex with her. But like one day I ask her how many guys have you slept with ! She said 20 or more ! Now I feel like she kinda a slut . I only slept with 2 girls and she the second one! What do I do I always think about all the other guys she bin with creeps me out !
She's still the same person she was before she shared that information with you. If you really like her, then I think its sad if you let her history affect whether or not you want to be with her. She's with YOU now, not any of those other guys.
Assuming she started having sex at 16, going through an average of 1 partner every month, I'd be surprised it wasn't more like 24. The question you have to ask is why would she tell you 20? To make you jealous? Was it a lie? Why would she tell the truth, does she like you that much, or why wouldn't she lie to you and say just a few? Its never as simple as it seems.