In the early stages of our relationship, my BF used to worry about this a lot and repeatedly told me that he couldn't understand what I saw in him, that I was out of his league, etc. I can promise you that as someone who has struggled with my own self-esteem issues, it absolutely stunned me to hear this. Because I felt the exact same way about him. When I first met him, I thought there was no way anything was going to come of my crush on him because he was just way too smart, too funny, too different to want to be with someone who was just kind of average. And then when we did start going out, I was desperately trying to be the "cool girlfriend", essentially putting on an act, terrified that he would leave me if I appeared too emotional/invested. That in turn made him afraid to show his feelings for me because he was put off by my "cool" act!

5 years down the road and we're now very comfortable with one another and no longer feel like we might lose one another if we make one false move. We've realized that we were judging one another and ourselves by totally arbitrary standards that don't really mean anything in the context of our relationship. We realized that neither of us is "better" or "in a higher league" than the other, we're both just perfect for one another.

Moral of the story: Stop putting your GF on a pedestal based on her previous partners and a list of qualities that people tell you are what make some people "better" than others. You both chose one another, and only you yourselves can determine what qualities are important in your relationship and how good you are for one another. Stop worrying. Be yourself - I guarantee you that she will catch on fairly early if you're putting on a "false front" for her (NOBODY is charming and funny all the time), which in turn will put pressure on her. Realize just how arbitrary your assessment of your own worth in relation to that of your GF is and how insignificant it is compared to a true emotional connection.