How Do I Get Over My Girlfriend's Past?

Okay we're 17 and I've had other girlfriends but I never slept with them, she on the other hand has slept with 5 people, two boyfriends, one FWB and 2 one night stands and honestly I personally find multiple partners gross and would like that number to be as low as possible but w/e, what's done is done. I tried ignoring everything, thinking that those guys were in the past and she's with me now, and it works emotionally, however whenever we get physically intimate I can't help but feel bad knowing that everything I'm doing, it's all been done before. is nothing new to her, she's used to it. She brought someone else to her bedroom, took her clothes off for someone else, made love to someone else and when she thinks about the guy who explored her body, it's not gonna me, while the feeling isn't mutual :/. We're not on an even playing field. If anyone has heard the song "brand new" by Drake, that's exactly how I feel. Anyone have some real advice to give?