Help getting over my girlfriend's ual past?

i have been dating my girl for around 3 months. it has now come to light that my girlfriend has had with her ex boyfriend. i find to be disgusting, repulsive, and an ultimate act of disrespect. she said she tried it once and hated it, it wasn't her idea and she didn't want to do it but she did it b/c she loved her ex. now that i know she has done it i can't look at her the same. it's almost like she's tainted in my eyes. every time i talk to her or see her i just don't see the girl that i fell for, i am almost embarred to know her. I don't want to feel this way about my girlfriend. I know i have a past too, but a relatively clean one. It's not that i'm upset that she was with another guy, it's just that my views on are just so awful that it makes me think of her in a bad way.