Sex isn't the Olympics. You're not always going to hook up with the best person and if you find a new person move on to them. Looks aren't everything. As Ben Franklin observed about having sex with older women "All cats are gray in the dark"
I've been in relationships with girls who had multiple partners who thought this way. They were sluts. (same goes for guys on the other side of the deal). I've also been with girls who had multiple partners who were extremely loyal.
Yes -- people who are uninhibited, risk-takers, and have poor judgment skills are not the kind for long-term relationships. But that set of people does not include everybody who has had multiple sex partners, even though all of those people are probably promiscuous. You're being silly.
It's much wiser to spend your time creating boundaries about how you deserve to be treated, not about what somebody's past is. Get out. Meet people. Date. Have sex if that is what comes natural to you. If you don't feel like it, don't have sex. But don't go berserko over past sex partners. You'll never compare up to the best of 20 other guys -- and if you think you have to, you don't understand what having a relationship means.