Most likely you are not physically appealing to her. If that is what you think is what is wrong with you, then it is most likely. Girls/women won't tell that truth to you. But my impression on this, is that you don't look the type she wants of a guy.
Looks is very important, shallow or not, everyone wants a mate that looks appealing.
If you think you don't look attractive, then it most likely true, there are no other opinion about yourself that is closer to the truth than yours.
It much harder for guys to get girls than the other way around. Girls gets it easy. Girls just wait for guys to come to them and then they choose, and even have the chance to play them, if they are bored with them, they just dump them.
It depends, if the guy is handsome, then it is very easy. Life is easy when you are beautiful. Life would be a hell if you are otherwise.