What should I do to keep someone I love loving me?

Two years ago I sucbed to love with someone younger than I am and with the same outlook in life just like me. As I increased my devotion to this little loving bird, she experienced the opposite and litlle by little lowered her feelings towards me unintentionally, however we both feel confortable with each other, with respect, we have incredible tender moments, we share values social and economic within the normal range, we both know what we want and what we dont want. We now believe on the saying of happy for no reason, because of that she tells me that she wants to love someone crazily, have bursting feelings of love, doing anything at anytime for that person, making life happier, ier, open and yet have a link that cannot be broken. However she tells now that her feelings for me has diminished considerably and she wants to move out in order to feel if, I really am the right person for her and that she will miss me. What should I do: let her go and not try or what? Please help.