In my head

Why does a man have to define a woman?
It's something that always flashes back into my mind and continuously makes me feel uneasy and uncomfortable. The question should be actually different why do so many women think that a man has to define them?..

It's obvoius that women's situation has changed over the last decades and we are getting more and more rights and I am not in any place to go into feminist debates partially because I don't feel I have the right knowledge to do so. 
I just keep thinking why so many women still define themselves through the men they are with. Even when they are barely in their 20's..  Don't get me wrong I am not criticising the situation of being a couple because I think it's one of the most beautiful things deciding to share your life with another person. But why do so many of us locate all our self esteem in our man.
Why do girls so easily give up first their girlfriends..friends, interests, hobbies, autonomy..
Don't modern guys want a woman that is a partner, someone who has a voice and is not just an echo.
I know it's a cliche but you must admit it: It's hard being a woman!
Take a look at Amanda de Cadenet series called The conversation. who talks with intelligent and strong women about how not to loose your own self. 

PS: the photo is completely irrelevant ahh the woman nature in me :)