I can understand where you're coming from, bro.
A while back I was seeing a young girl (17), FYI legal in the UK!

For about two weeks, I thought she was really cool and she was very pretty, it was all cool. One day at lunch at a Chinese restaurant she gave away, that she may have had many previous sexual partners and got very defensive. I got very obsessive. Initially I was very concerned as I had unprotected sex, yet she assured me that she had been tested and subsequently I got tested and was fine. Yet, it did not stop me from being obsessed with finding out how many it was. My whole opinion of her had changed from when I first met her. I think one of the reasons it concerned me was she was always defensive and looked shameful whenever anything related was brought up. Because of my restless pointless, toxic thoughts of her past, she revealed to me that she had slept with a married man at her work and however common this maybe in reality, it made her feel like shit. She was a really cool girl, but she had low self esteem and tended to be quite needy, so we broke up later on.
This was all before my knowledge of the community and I think we all know those amazing epiphanies that re-framed our view of dating and indeed life, that pick-up has brought to our life. I would like it to be known that a girls sexual past has zero impact on my view of them, in fact I quite enjoy and respect a free spirit, with all the social constraints they have, not to mention the lack of LMR issues.
Moral of the story: change your view or you face making a lot of girls unhappy!
Wordsworth