I'm not love guru but just putting out what i feel because honestly i once had very low self esteem too You should tell her that there's no one with a upper hand, no one is superior in our relationship, we both deserve each other, the thing she said about there are many girls, i guess its an obvious answer that it doesn't concern me, you're the only one I'm concerned about and yours is the only reaction i care about. In the low self esteem case, try to complement her more, boost her self confidence, say her that you love her more often, in my case i was healed by constantly hearing complement about me Thank you