Defined by a relationship?

Well, when I was been asked twenty questions by some of my students they asked if I was in a relationship?  I told them they I had a boyfriend. They looked at me like I had won the lottery. Which I guess in a sense I have I found some one who can live with my many neurosis and loves me any way.  However, for some of the teenagers it seemed like being in a relationship was a defining part of their identity.
I guess I find this sort of clingy aspect weird because I have always viewed it that I was my own person out of said relationship.  I still like to do my own things, watch my own shows, and hell even hog the bed and still in some sense want my own space. Its not that I don’t like this person in this space with me, it makes it better and its nice to have someone that banters and keeps up, if not I would be both lonely and bored, and frankly he is one of the few people I know who really gets me.  I just wonder why these teenager girls think there lives need to be defined by whether or not they have a boyfriend? I wonder why they are not focused on volunteering, going to college, or in some shape or form thinking about their future. Or at the very least if they do have a boyfriend their grades should not suffer in the process.
Also I think the reason this infatuation towards a guy is so foreign to me is because I have the anomaly of being in a relationship longer than most people have been married and I have an overwhelming fear of commitment and intimacy.  It took me tell about six months ago to be comfortable with the idea of being engaged.  The one good thing is my boyfriend has similar fears as I do so combined we might make a normal healthy person in a relationship.  We both have our own reasons for feeling this way but we get each other none the less.   So all this reflection has me wondering for those single and coupled up do you ever feel defined by your relationship or can you be your own person even while being in a relationship?  And is their some grey area between these two point of views?