dont worry all guys feel that way about their gf's its just a natural thing where we have the ambition to be control or we get worried. There is probly nothing wrong with your relationship and you have no need to be sad.
Different things you could do are
-actually asking her if she loves you/telling her your feelings
-just spend some time together without fooling around and just doing things together like going to the mall or rent a movie she likes
-watch out if she is flirting with other guys
but really dont worry, you are fine and should enjoy your time together before you both move on instead of worrying what could happen.
May the wind always be at your back
and the sun upon your face,
and the winds of destiny carry you aloft
to dance with the stars...