To think that you are the best your partner ever had is ego and nothing more. To be upset because you think you may not be the best your partner ever had is also your ego giving you hell. To be unable to realize that you may not be the best when it comes to sexual passion but you are the best in all ways, including sexual satifiaction, is immaturity.
Stop wondering about this and enjoy what you have in the moment. Take her compliment as you being the best she ever had and enjoy without ego. You are causing unnecessary angst in your own life.
The willingness to accept responsibility for ones own life is the source from which self-respect springs. ~Joan Didion